propagate_mnt() does not attach anything to mounts created during
propagate_mnt() itself. What's more, anything on ->mnt_slave_list
of such new mount must also be new, so we don't need to even look
there.
When move_mount() had been introduced, we've got an additional
class of mounts to skip - if we are moving from anon namespace,
we do not want to propagate to mounts we are moving (i.e. all
mounts in that anon namespace).
Unfortunately, the part about "everything on their ->mnt_slave_list
will also be ignorable" is not true - if we have propagation graph
A -> B -> C
and do OPEN_TREE_CLONE open_tree() of B, we get
A -> [B <-> B'] -> C
as propagation graph, where B' is a clone of B in our detached tree.
Making B private will result in
A -> B' -> C
C still gets propagation from A, as it would after making B private
if we hadn't done that open_tree(), but now the propagation goes
through B'. Trying to move_mount() our detached tree on subdirectory
in A should have
* moved B' on that subdirectory in A
* skipped the corresponding subdirectory in B' itself
* copied B' on the corresponding subdirectory in C.
As it is, the logics in propagation_next() and friends ends up
skipping propagation into C, since it doesn't consider anything
downstream of B'.
IOW, walking the propagation graph should only skip the ->mnt_slave_list
of new mounts; the only places where the check for "in that one
anon namespace" are applicable are propagate_one() (where we should
treat that as the same kind of thing as "mountpoint we are looking
at is not visible in the mount we are looking at") and
propagation_would_overmount(). The latter is better dealt with
in the caller (can_move_mount_beneath()); on the first call of
propagation_would_overmount() the test is always false, on the
second it is always true in "move from anon namespace" case and
always false in "move within our namespace" one, so it's easier
to just use check_mnt() before bothering with the second call and
be done with that.
Fixes: 064fe6e233 ("mount: handle mount propagation for detached mount trees")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
as it is, a failed move_mount(2) from anon namespace breaks
all further propagation into that namespace, including normal
mounts in non-anon namespaces that would otherwise propagate
there.
Fixes: 064fe6e233 ("mount: handle mount propagation for detached mount trees")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
do_umount() analogue of the race fixed in 119e1ef80e "fix
__legitimize_mnt()/mntput() race". Here we want to make sure that
if __legitimize_mnt() doesn't notice our lock_mount_hash(), we will
notice their refcount increment. Harder to hit than mntput_no_expire()
one, fortunately, and consequences are milder (sync umount acting
like umount -l on a rare race with RCU pathwalk hitting at just the
wrong time instead of use-after-free galore mntput_no_expire()
counterpart used to be hit). Still a bug...
Fixes: 48a066e72d ("RCU'd vfsmounts")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... or we risk stealing final mntput from sync umount - raising mnt_count
after umount(2) has verified that victim is not busy, but before it
has set MNT_SYNC_UMOUNT; in that case __legitimize_mnt() doesn't see
that it's safe to quietly undo mnt_count increment and leaves dropping
the reference to caller, where it'll be a full-blown mntput().
Check under mount_lock is needed; leaving the current one done before
taking that makes no sense - it's nowhere near common enough to bother
with.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Normally do_lock_mount(path, _) is locking a mountpoint pinned by
*path and at the time when matching unlock_mount() unlocks that
location it is still pinned by the same thing.
Unfortunately, for 'beneath' case it's no longer that simple -
the object being locked is not the one *path points to. It's the
mountpoint of path->mnt. The thing is, without sufficient locking
->mnt_parent may change under us and none of the locks are held
at that point. The rules are
* mount_lock stabilizes m->mnt_parent for any mount m.
* namespace_sem stabilizes m->mnt_parent, provided that
m is mounted.
* if either of the above holds and refcount of m is positive,
we are guaranteed the same for refcount of m->mnt_parent.
namespace_sem nests inside inode_lock(), so do_lock_mount() has
to take inode_lock() before grabbing namespace_sem. It does
recheck that path->mnt is still mounted in the same place after
getting namespace_sem, and it does take care to pin the dentry.
It is needed, since otherwise we might end up with racing mount --move
(or umount) happening while we were getting locks; in that case
dentry would no longer be a mountpoint and could've been evicted
on memory pressure along with its inode - not something you want
when grabbing lock on that inode.
However, pinning a dentry is not enough - the matching mount is
also pinned only by the fact that path->mnt is mounted on top it
and at that point we are not holding any locks whatsoever, so
the same kind of races could end up with all references to
that mount gone just as we are about to enter inode_lock().
If that happens, we are left with filesystem being shut down while
we are holding a dentry reference on it; results are not pretty.
What we need to do is grab both dentry and mount at the same time;
that makes inode_lock() safe *and* avoids the problem with fs getting
shut down under us. After taking namespace_sem we verify that
path->mnt is still mounted (which stabilizes its ->mnt_parent) and
check that it's still mounted at the same place. From that point
on to the matching namespace_unlock() we are guaranteed that
mount/dentry pair we'd grabbed are also pinned by being the mountpoint
of path->mnt, so we can quietly drop both the dentry reference (as
the current code does) and mnt one - it's OK to do under namespace_sem,
since we are not dropping the final refs.
That solves the problem on do_lock_mount() side; unlock_mount()
also has one, since dentry is guaranteed to stay pinned only until
the namespace_unlock(). That's easy to fix - just have inode_unlock()
done earlier, while it's still pinned by mp->m_dentry.
Fixes: 6ac3928156 "fs: allow to mount beneath top mount" # v6.5+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christian Brauner <brauner@kernel.org>
In commit b73ec10a45 ("fs: add fastpath for dissolve_on_fput()"),
the namespace_{lock,unlock} has been replaced with scoped_guard
using the namespace_sem. This however now also skips processing of
'unmounted' list in namespace_unlock(), and mount is not (immediately)
cleaned up.
For example, this causes LTP move_mount02 fail:
...
move_mount02.c:80: TPASS: invalid-from-fd: move_mount() failed as expected: EBADF (9)
move_mount02.c:80: TPASS: invalid-from-path: move_mount() failed as expected: ENOENT (2)
move_mount02.c:80: TPASS: invalid-to-fd: move_mount() failed as expected: EBADF (9)
move_mount02.c:80: TPASS: invalid-to-path: move_mount() failed as expected: ENOENT (2)
move_mount02.c:80: TPASS: invalid-flags: move_mount() failed as expected: EINVAL (22)
tst_test.c:1833: TINFO: === Testing on ext3 ===
tst_test.c:1170: TINFO: Formatting /dev/loop0 with ext3 opts='' extra opts=''
mke2fs 1.47.2 (1-Jan-2025)
/dev/loop0 is apparently in use by the system; will not make a filesystem here!
tst_test.c:1170: TBROK: mkfs.ext3 failed with exit code 1
The test makes number of move_mount() calls but these are all designed to fail
with specific errno. Even after test, 'losetup -d' can't detach loop device.
Define a new guard for dissolve_on_fput, that will use namespace_{lock,unlock}.
Fixes: b73ec10a45 ("fs: add fastpath for dissolve_on_fput()")
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Link: https://lore.kernel.org/cad2f042b886bf0ced3d8e3aff120ec5e0125d61.1744297468.git.jstancek@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Don't use a scoped guard that only protects the next statement.
Use a regular guard to make sure that the namespace semaphore is held
across the whole function.
Signed-off-by: Christian Brauner <brauner@kernel.org>
Reported-by: Leon Romanovsky <leon@kernel.org>
Link: https://lore.kernel.org/all/20250401170715.GA112019@unreal/
Fixes: db04662e2f ("fs: allow detached mounts in clone_private_mount()")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.
Move the conflicting declaration to the end of the structure. Notice
that `struct statmount` is a flexible structure --a structure that
contains a flexible-array member.
Fix the following warning:
fs/namespace.c:5329:26: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
Signed-off-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/Z-SZKNdCiAkVJvqm@kspp
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'vfs-6.15-rc1.mount.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs mount namespace updates from Christian Brauner:
"This expands the ability of anonymous mount namespaces:
- Creating detached mounts from detached mounts
Currently, detached mounts can only be created from attached
mounts. This limitaton prevents various use-cases. For example, the
ability to mount a subdirectory without ever having to make the
whole filesystem visible first.
The current permission modelis:
(1) Check that the caller is privileged over the owning user
namespace of it's current mount namespace.
(2) Check that the caller is located in the mount namespace of the
mount it wants to create a detached copy of.
While it is not strictly necessary to do it this way it is
consistently applied in the new mount api. This model will also be
used when allowing the creation of detached mount from another
detached mount.
The (1) requirement can simply be met by performing the same check
as for the non-detached case, i.e., verify that the caller is
privileged over its current mount namespace.
To meet the (2) requirement it must be possible to infer the origin
mount namespace that the anonymous mount namespace of the detached
mount was created from.
The origin mount namespace of an anonymous mount is the mount
namespace that the mounts that were copied into the anonymous mount
namespace originate from.
In order to check the origin mount namespace of an anonymous mount
namespace the sequence number of the original mount namespace is
recorded in the anonymous mount namespace.
With this in place it is possible to perform an equivalent check
(2') to (2). The origin mount namespace of the anonymous mount
namespace must be the same as the caller's mount namespace. To
establish this the sequence number of the caller's mount namespace
and the origin sequence number of the anonymous mount namespace are
compared.
The caller is always located in a non-anonymous mount namespace
since anonymous mount namespaces cannot be setns()ed into. The
caller's mount namespace will thus always have a valid sequence
number.
The owning namespace of any mount namespace, anonymous or
non-anonymous, can never change. A mount attached to a
non-anonymous mount namespace can never change mount namespace.
If the sequence number of the non-anonymous mount namespace and the
origin sequence number of the anonymous mount namespace match, the
owning namespaces must match as well.
Hence, the capability check on the owning namespace of the caller's
mount namespace ensures that the caller has the ability to copy the
mount tree.
- Allow mount detached mounts on detached mounts
Currently, detached mounts can only be mounted onto attached
mounts. This limitation makes it impossible to assemble a new
private rootfs and move it into place. Instead, a detached tree
must be created, attached, then mounted open and then either moved
or detached again. Lift this restriction.
In order to allow mounting detached mounts onto other detached
mounts the same permission model used for creating detached mounts
from detached mounts can be used (cf. above).
Allowing to mount detached mounts onto detached mounts leaves three
cases to consider:
(1) The source mount is an attached mount and the target mount is
a detached mount. This would be equivalent to moving a mount
between different mount namespaces. A caller could move an
attached mount to a detached mount. The detached mount can now
be freely attached to any mount namespace. This changes the
current delegatioh model significantly for no good reason. So
this will fail.
(2) Anonymous mount namespaces are always attached fully, i.e., it
is not possible to only attach a subtree of an anoymous mount
namespace. This simplifies the implementation and reasoning.
Consequently, if the anonymous mount namespace of the source
detached mount and the target detached mount are the identical
the mount request will fail.
(3) The source mount's anonymous mount namespace is different from
the target mount's anonymous mount namespace.
In this case the source anonymous mount namespace of the
source mount tree must be freed after its mounts have been
moved to the target anonymous mount namespace. The source
anonymous mount namespace must be empty afterwards.
By allowing to mount detached mounts onto detached mounts a caller
may do the following:
fd_tree1 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE)
fd_tree2 = open_tree(-EBADF, "/tmp", OPEN_TREE_CLONE)
fd_tree1 and fd_tree2 refer to two different detached mount trees
that belong to two different anonymous mount namespace.
It is important to note that fd_tree1 and fd_tree2 both refer to
the root of their respective anonymous mount namespaces.
By allowing to mount detached mounts onto detached mounts the
caller may now do:
move_mount(fd_tree1, "", fd_tree2, "",
MOVE_MOUNT_F_EMPTY_PATH | MOVE_MOUNT_T_EMPTY_PATH)
This will cause the detached mount referred to by fd_tree1 to be
mounted on top of the detached mount referred to by fd_tree2.
Thus, the detached mount fd_tree1 is moved from its separate
anonymous mount namespace into fd_tree2's anonymous mount
namespace.
It also means that while fd_tree2 continues to refer to the root of
its respective anonymous mount namespace fd_tree1 doesn't anymore.
This has the consequence that only fd_tree2 can be moved to another
anonymous or non-anonymous mount namespace. Moving fd_tree1 will
now fail as fd_tree1 doesn't refer to the root of an anoymous mount
namespace anymore.
Now fd_tree1 and fd_tree2 refer to separate detached mount trees
referring to the same anonymous mount namespace.
This is conceptually fine. The new mount api does allow for this to
happen already via:
mount -t tmpfs tmpfs /mnt
mkdir -p /mnt/A
mount -t tmpfs tmpfs /mnt/A
fd_tree3 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE | AT_RECURSIVE)
fd_tree4 = open_tree(-EBADF, "/mnt/A", 0)
Both fd_tree3 and fd_tree4 refer to two different detached mount
trees but both detached mount trees refer to the same anonymous
mount namespace. An as with fd_tree1 and fd_tree2, only fd_tree3
may be moved another mount namespace as fd_tree3 refers to the root
of the anonymous mount namespace just while fd_tree4 doesn't.
However, there's an important difference between the
fd_tree3/fd_tree4 and the fd_tree1/fd_tree2 example.
Closing fd_tree4 and releasing the respective struct file will have
no further effect on fd_tree3's detached mount tree.
However, closing fd_tree3 will cause the mount tree and the
respective anonymous mount namespace to be destroyed causing the
detached mount tree of fd_tree4 to be invalid for further mounting.
By allowing to mount detached mounts on detached mounts as in the
fd_tree1/fd_tree2 example both struct files will affect each other.
Both fd_tree1 and fd_tree2 refer to struct files that have
FMODE_NEED_UNMOUNT set.
To handle this we use the fact that @fd_tree1 will have a parent
mount once it has been attached to @fd_tree2.
When dissolve_on_fput() is called the mount that has been passed in
will refer to the root of the anonymous mount namespace. If it
doesn't it would mean that mounts are leaked. So before allowing to
mount detached mounts onto detached mounts this would be a bug.
Now that detached mounts can be mounted onto detached mounts it
just means that the mount has been attached to another anonymous
mount namespace and thus dissolve_on_fput() must not unmount the
mount tree or free the anonymous mount namespace as the file
referring to the root of the namespace hasn't been closed yet.
If it had been closed yet it would be obvious because the mount
namespace would be NULL, i.e., the @fd_tree1 would have already
been unmounted. If @fd_tree1 hasn't been unmounted yet and has a
parent mount it is safe to skip any cleanup as closing @fd_tree2
will take care of all cleanup operations.
- Allow mount propagation for detached mount trees
In commit ee2e3f5062 ("mount: fix mounting of detached mounts
onto targets that reside on shared mounts") I fixed a bug where
propagating the source mount tree of an anonymous mount namespace
into a target mount tree of a non-anonymous mount namespace could
be used to trigger an integer overflow in the non-anonymous mount
namespace causing any new mounts to fail.
The cause of this was that the propagation algorithm was unable to
recognize mounts from the source mount tree that were already
propagated into the target mount tree and then reappeared as
propagation targets when walking the destination propagation mount
tree.
When fixing this I disabled mount propagation into anonymous mount
namespaces. Make it possible for anonymous mount namespace to
receive mount propagation events correctly. This is now also a
correctness issue now that we allow mounting detached mount trees
onto detached mount trees.
Mark the source anonymous mount namespace with MNTNS_PROPAGATING
indicating that all mounts belonging to this mount namespace are
currently in the process of being propagated and make the
propagation algorithm discard those if they appear as propagation
targets"
* tag 'vfs-6.15-rc1.mount.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (21 commits)
selftests: test subdirectory mounting
selftests: add test for detached mount tree propagation
fs: namespace: fix uninitialized variable use
mount: handle mount propagation for detached mount trees
fs: allow creating detached mounts from fsmount() file descriptors
selftests: seventh test for mounting detached mounts onto detached mounts
selftests: sixth test for mounting detached mounts onto detached mounts
selftests: fifth test for mounting detached mounts onto detached mounts
selftests: fourth test for mounting detached mounts onto detached mounts
selftests: third test for mounting detached mounts onto detached mounts
selftests: second test for mounting detached mounts onto detached mounts
selftests: first test for mounting detached mounts onto detached mounts
fs: mount detached mounts onto detached mounts
fs: support getname_maybe_null() in move_mount()
selftests: create detached mounts from detached mounts
fs: create detached mounts from detached mounts
fs: add may_copy_tree()
fs: add fastpath for dissolve_on_fput()
fs: add assert for move_mount()
fs: add mnt_ns_empty() helper
...
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Merge tag 'vfs-6.15-rc1.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs mount updates from Christian Brauner:
- Mount notifications
The day has come where we finally provide a new api to listen for
mount topology changes outside of /proc/<pid>/mountinfo. A mount
namespace file descriptor can be supplied and registered with
fanotify to listen for mount topology changes.
Currently notifications for mount, umount and moving mounts are
generated. The generated notification record contains the unique
mount id of the mount.
The listmount() and statmount() api can be used to query detailed
information about the mount using the received unique mount id.
This allows userspace to figure out exactly how the mount topology
changed without having to generating diffs of /proc/<pid>/mountinfo
in userspace.
- Support O_PATH file descriptors with FSCONFIG_SET_FD in the new mount
api
- Support detached mounts in overlayfs
Since last cycle we support specifying overlayfs layers via file
descriptors. However, we don't allow detached mounts which means
userspace cannot user file descriptors received via
open_tree(OPEN_TREE_CLONE) and fsmount() directly. They have to
attach them to a mount namespace via move_mount() first.
This is cumbersome and means they have to undo mounts via umount().
Allow them to directly use detached mounts.
- Allow to retrieve idmappings with statmount
Currently it isn't possible to figure out what idmapping has been
attached to an idmapped mount. Add an extension to statmount() which
allows to read the idmapping from the mount.
- Allow creating idmapped mounts from mounts that are already idmapped
So far it isn't possible to allow the creation of idmapped mounts
from already idmapped mounts as this has significant lifetime
implications. Make the creation of idmapped mounts atomic by allow to
pass struct mount_attr together with the open_tree_attr() system call
allowing to solve these issues without complicating VFS lookup in any
way.
The system call has in general the benefit that creating a detached
mount and applying mount attributes to it becomes an atomic operation
for userspace.
- Add a way to query statmount() for supported options
Allow userspace to query which mount information can be retrieved
through statmount().
- Allow superblock owners to force unmount
* tag 'vfs-6.15-rc1.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (21 commits)
umount: Allow superblock owners to force umount
selftests: add tests for mount notification
selinux: add FILE__WATCH_MOUNTNS
samples/vfs: fix printf format string for size_t
fs: allow changing idmappings
fs: add kflags member to struct mount_kattr
fs: add open_tree_attr()
fs: add copy_mount_setattr() helper
fs: add vfs_open_tree() helper
statmount: add a new supported_mask field
samples/vfs: add STATMOUNT_MNT_{G,U}IDMAP
selftests: add tests for using detached mount with overlayfs
samples/vfs: check whether flag was raised
statmount: allow to retrieve idmappings
uidgid: add map_id_range_up()
fs: allow detached mounts in clone_private_mount()
selftests/overlayfs: test specifying layers as O_PATH file descriptors
fs: support O_PATH fds with FSCONFIG_SET_FD
vfs: add notifications for mount attach and detach
fanotify: notify on mount attach and detach
...
Loosen the permission check on forced umount to allow users holding
CAP_SYS_ADMIN privileges in namespaces that are privileged with respect
to the userns that originally mounted the filesystem.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Link: https://lore.kernel.org/r/12f212d4ef983714d065a6bb372fbb378753bf4c.1742315194.git.trond.myklebust@hammerspace.com
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
In commit ee2e3f5062 ("mount: fix mounting of detached mounts onto
targets that reside on shared mounts") I fixed a bug where propagating
the source mount tree of an anonymous mount namespace into a target
mount tree of a non-anonymous mount namespace could be used to trigger
an integer overflow in the non-anonymous mount namespace causing any new
mounts to fail.
The cause of this was that the propagation algorithm was unable to
recognize mounts from the source mount tree that were already propagated
into the target mount tree and then reappeared as propagation targets
when walking the destination propagation mount tree.
When fixing this I disabled mount propagation into anonymous mount
namespaces. Make it possible for anonymous mount namespace to receive
mount propagation events correctly. This is no also a correctness issue
now that we allow mounting detached mount trees onto detached mount
trees.
Mark the source anonymous mount namespace with MNTNS_PROPAGATING
indicating that all mounts belonging to this mount namespace are
currently in the process of being propagated and make the propagation
algorithm discard those if they appear as propagation targets.
Link: https://lore.kernel.org/r/20250225-work-mount-propagation-v1-1-e6e3724500eb@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
clang correctly notices that the 'uflags' variable initialization
only happens in some cases:
fs/namespace.c:4622:6: error: variable 'uflags' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
4622 | if (flags & MOVE_MOUNT_F_EMPTY_PATH) uflags = AT_EMPTY_PATH;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
fs/namespace.c:4623:48: note: uninitialized use occurs here
4623 | from_name = getname_maybe_null(from_pathname, uflags);
| ^~~~~~
fs/namespace.c:4622:2: note: remove the 'if' if its condition is always true
4622 | if (flags & MOVE_MOUNT_F_EMPTY_PATH) uflags = AT_EMPTY_PATH;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Fixes: b1e9423d65e3 ("fs: support getname_maybe_null() in move_mount()")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250226081201.1876195-1-arnd@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
The previous patch series only enabled the creation of detached mounts
from detached mounts that were created via open_tree(). In such cases we
know that the origin sequence number for the newly created anonymous
mount namespace will be set to the sequence number of the mount
namespace the source mount belonged to.
But fsmount() creates an anonymous mount namespace that does not have an
origin mount namespace as the anonymous mount namespace was derived from
a filesystem context created via fsopen().
Account for this case and allow the creation of detached mounts from
mounts created via fsmount(). Consequently, any such detached mount
created from an fsmount() mount will also have a zero origin sequence
number.
This allows to mount subdirectories without ever having to expose the
filesystem to a a non-anonymous mount namespace:
fd_context = sys_fsopen("tmpfs", 0);
sys_fsconfig(fd_context, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
fd_tmpfs = sys_fsmount(fd_context, 0, 0);
mkdirat(fd_tmpfs, "subdir", 0755);
fd_tree = sys_open_tree(fd_tmpfs, "subdir", OPEN_TREE_CLONE);
sys_move_mount(fd_tree, "", -EBADF, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
Signed-off-by: Christian Brauner <brauner@kernel.org>
Currently, detached mounts can only be mounted onto attached mounts.
This limitation makes it impossible to assemble a new private rootfs and
move it into place. That's an extremely powerful concept for container
and service workloads that we should support.
Right now, a detached tree must be created, attached, then it can gain
additional mounts and then it can either be moved (if it doesn't reside
under a shared mount) or a detached mount created again. Lift this
restriction.
In order to allow mounting detached mounts onto other detached mounts
the same permission model used for creating detached mounts from
detached mounts can be used:
(1) Check that the caller is privileged over the owning user namespace
of it's current mount namespace.
(2) Check that the caller is located in the mount namespace of the mount
it wants to create a detached copy of.
The origin mount namespace of the anonymous mount namespace must be the
same as the caller's mount namespace. To establish this the sequence
number of the caller's mount namespace and the origin sequence number of
the anonymous mount namespace are compared.
The caller is always located in a non-anonymous mount namespace since
anonymous mount namespaces cannot be setns()ed into. The caller's mount
namespace will thus always have a valid sequence number.
The owning namespace of any mount namespace, anonymous or non-anonymous,
can never change. A mount attached to a non-anonymous mount namespace
can never change mount namespace.
If the sequence number of the non-anonymous mount namespace and the
origin sequence number of the anonymous mount namespace match, the
owning namespaces must match as well.
Hence, the capability check on the owning namespace of the caller's
mount namespace ensures that the caller has the ability to attach the
mount tree.
Link: https://lore.kernel.org/r/20250221-brauner-open_tree-v1-9-dbcfcb98c676@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add the ability to create detached mounts from detached mounts.
Currently, detached mounts can only be created from attached mounts.
This limitaton prevents various use-cases. For example, the ability to
mount a subdirectory without ever having to make the whole filesystem
visible first.
The current permission model for the OPEN_TREE_CLONE flag of the
open_tree() system call is:
(1) Check that the caller is privileged over the owning user namespace
of it's current mount namespace.
(2) Check that the caller is located in the mount namespace of the mount
it wants to create a detached copy of.
While it is not strictly necessary to do it this way it is consistently
applied in the new mount api. This model will also be used when allowing
the creation of detached mount from another detached mount.
The (1) requirement can simply be met by performing the same check as
for the non-detached case, i.e., verify that the caller is privileged
over its current mount namespace.
To meet the (2) requirement it must be possible to infer the origin
mount namespace that the anonymous mount namespace of the detached mount
was created from.
The origin mount namespace of an anonymous mount is the mount namespace
that the mounts that were copied into the anonymous mount namespace
originate from.
The origin mount namespace of the anonymous mount namespace must be the
same as the caller's mount namespace. To establish this the sequence
number of the caller's mount namespace and the origin sequence number of
the anonymous mount namespace are compared.
The caller is always located in a non-anonymous mount namespace since
anonymous mount namespaces cannot be setns()ed into. The caller's mount
namespace will thus always have a valid sequence number.
The owning namespace of any mount namespace, anonymous or non-anonymous,
can never change. A mount attached to a non-anonymous mount namespace
can never change mount namespace.
If the sequence number of the non-anonymous mount namespace and the
origin sequence number of the anonymous mount namespace match, the
owning namespaces must match as well.
Hence, the capability check on the owning namespace of the caller's
mount namespace ensures that the caller has the ability to copy the
mount tree.
Link: https://lore.kernel.org/r/20250221-brauner-open_tree-v1-6-dbcfcb98c676@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Instead of acquiring the namespace semaphore and the mount lock
everytime we close a file with FMODE_NEED_UNMOUNT set add a fastpath
that checks whether we need to at all. Most of the time the caller will
have attached the mount to the filesystem hierarchy and there's nothing
to do.
Link: https://lore.kernel.org/r/20250221-brauner-open_tree-v1-4-dbcfcb98c676@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Christian Brauner <brauner@kernel.org> says:
Currently, it isn't possible to change the idmapping of an idmapped
mount. This is becoming an obstacle for various use-cases.
/* idmapped home directories with systemd-homed */
On newer systems /home is can be an idmapped mount such that each file
on disk is owned by 65536 and a subfolder exists for foreign id ranges
such as containers. For example, a home directory might look like this
(using an arbitrary folder as an example):
user1@localhost:~/data/mount-idmapped$ ls -al /data/
total 16
drwxrwxrwx 1 65536 65536 36 Jan 27 12:15 .
drwxrwxr-x 1 root root 184 Jan 27 12:06 ..
-rw-r--r-- 1 65536 65536 0 Jan 27 12:07 aaa
-rw-r--r-- 1 65536 65536 0 Jan 27 12:07 bbb
-rw-r--r-- 1 65536 65536 0 Jan 27 12:07 cc
drwxr-xr-x 1 2147352576 2147352576 0 Jan 27 19:06 containers
When logging in home is mounted as an idmapped mount with the following
idmappings:
65536:$(id -u):1 // uid mapping
65536:$(id -g):1 // gid mapping
2147352576:2147352576:65536 // uid mapping
2147352576:2147352576:65536 // gid mapping
So for a user with uid/gid 1000 an idmapped /home would like like this:
user1@localhost:~/data/mount-idmapped$ ls -aln /mnt/
total 16
drwxrwxrwx 1 1000 1000 36 Jan 27 12:15 .
drwxrwxr-x 1 0 0 184 Jan 27 12:06 ..
-rw-r--r-- 1 1000 1000 0 Jan 27 12:07 aaa
-rw-r--r-- 1 1000 1000 0 Jan 27 12:07 bbb
-rw-r--r-- 1 1000 1000 0 Jan 27 12:07 cc
drwxr-xr-x 1 2147352576 2147352576 0 Jan 27 19:06 containers
In other words, 65536 is mapped to the user's uid/gid and the range
2147352576 up to 2147352576 + 65536 is an identity mapping for
containers.
When a container is started a transient uid/gid range is allocated
outside of both mappings of the idmapped mount. For example, the
container might get the idmapping:
$ cat /proc/1742611/uid_map
0 537985024 65536
This container will be allowed to write to disk within the allocated
foreign id range 2147352576 to 2147352576 + 65536. To do this an
idmapped mount must be created from an already idmapped mount such that:
- The mappings for the user's uid/gid must be dropped, i.e., the
following mappings are removed:
65536:$(id -u):1 // uid mapping
65536:$(id -g):1 // gid mapping
- A mapping for the transient uid/gid range to the foreign uid/gid range
is added:
2147352576:537985024:65536
In combination this will mean that the container will write to disk
within the foreign id range 2147352576 to 2147352576 + 65536.
/* nested containers */
When the outer container makes use of idmapped mounts it isn't posssible
to create an idmapped mount for the inner container with a differen
idmapping from the outer container's idmapped mount.
There are other usecases and the two above just serve as an illustration
of the problem.
This patchset makes it possible to create a new idmapped mount from an
already idmapped mount. It aims to adhere to current performance
constraints and requirements:
- Idmapped mounts aim to have near zero performance implications for
path lookup. That is why no refernce counting, locking or any other
mechanism can be required that would impact performance.
This works be ensuring that a regular mount transitions to an idmapped
mount once going from a static nop_mnt_idmap mapping to a non-static
idmapping.
- The idmapping of a mount change anymore for the lifetime of the mount
afterwards. This not just avoids UAF issues it also avoids pitfalls
such as generating non-matching uid/gid values.
Changing idmappings could be solved by:
- Idmappings could simply be reference counted (above the simple
reference count when sharing them across multiple mounts).
This would require pairing mnt_idmap_get() with mnt_idmap_put() which
would end up being sprinkled everywhere into the VFS and some
filesystems that access idmappings directly.
It wouldn't just be quite ugly and introduce new complexity it would
have a noticeable performance impact.
- Idmappings could gain RCU protection. This would help the LOOKUP_RCU
case and avoids taking reference counts under RCU.
When not under LOOKUP_RCU reference counts need to be acquired on each
idmapping. This would require pairing mnt_idmap_get() with
mnt_idmap_put() which would end up being sprinkled everywhere into the
VFS and some filesystems that access idmappings directly.
This would have the same downsides as mentioned earlier.
- The earlier solutions work by updating the mnt->mnt_idmap pointer with
the new idmapping. Instead of this it would be possible to change the
idmapping itself to avoid UAF issues.
To do this a sequence counter would have to be added to struct mount.
When retrieving the idmapping to generate uid/gid values the sequence
counter would need to be sampled and the generation of the uid/gid
would spin until the update of the idmap is finished.
This has problems as well but the biggest issue will be that this can
lead to inconsistent permission checking and inconsistent uid/gid
pairs even more than this is already possible today. Specifically,
during creation it could happen that:
idmap = mnt_idmap(mnt);
inode_permission(idmap, ...);
may_create(idmap);
// create file with uid/gid based on @idmap
in between the permission checking and the generation of the uid/gid
value the idmapping could change leading to the permission checking
and uid/gid value that is actually used to create a file on disk being
out of sync.
Similarly if two values are generated like:
idmap = mnt_idmap(mnt)
vfsgid = make_vfsgid(idmap);
// idmapping gets update concurrently
vfsuid = make_vfsuid(idmap);
@vfsgid and @vfsuid could be out of sync if the idmapping was changed
in between. The generation of vfsgid/vfsuid could span a lot of
codelines so to guard against this a sequence count would have to be
passed around.
The performance impact of this solutio are less clear but very likely
not zero.
- Using SRCU similar to fanotify that can sleep. I find that not just
ugly but it would have memory consumption implications and is overall
pretty ugly.
/* solution */
So, to avoid all of these pitfalls creating an idmapped mount from an
already idmapped mount will be done atomically, i.e., a new detached
mount is created and a new set of mount properties applied to it without
it ever having been exposed to userspace at all.
This can be done in two ways. A new flag to open_tree() is added
OPEN_TREE_CLEAR_IDMAP that clears the old idmapping and returns a mount
that isn't idmapped. And then it is possible to set mount attributes on
it again including creation of an idmapped mount.
This has the consequence that a file descriptor must exist in userspace
that doesn't have any idmapping applied and it will thus never work in
unpriviledged scenarios. As a container would be able to remove the
idmapping of the mount it has been given. That should be avoided.
Instead, we add open_tree_attr() which works just like open_tree() but
takes an optional struct mount_attr parameter. This is useful beyond
idmappings as it fills a gap where a mount never exists in userspace
without the necessary mount properties applied.
This is particularly useful for mount options such as
MOUNT_ATTR_{RDONLY,NOSUID,NODEV,NOEXEC}.
To create a new idmapped mount the following works:
// Create a first idmapped mount
struct mount_attr attr = {
.attr_set = MOUNT_ATTR_IDMAP
.userns_fd = fd_userns
};
fd_tree = open_tree(-EBADF, "/", OPEN_TREE_CLONE, &attr, sizeof(attr));
move_mount(fd_tree, "", -EBADF, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
// Create a second idmapped mount from the first idmapped mount
attr.attr_set = MOUNT_ATTR_IDMAP;
attr.userns_fd = fd_userns2;
fd_tree2 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE, &attr, sizeof(attr));
// Create a second non-idmapped mount from the first idmapped mount:
memset(&attr, 0, sizeof(attr));
attr.attr_clr = MOUNT_ATTR_IDMAP;
fd_tree2 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE, &attr, sizeof(attr));
* patches from https://lore.kernel.org/r/20250128-work-mnt_idmap-update-v2-v1-0-c25feb0d2eb3@kernel.org:
fs: allow changing idmappings
fs: add kflags member to struct mount_kattr
fs: add open_tree_attr()
fs: add copy_mount_setattr() helper
fs: add vfs_open_tree() helper
Link: https://lore.kernel.org/r/20250128-work-mnt_idmap-update-v2-v1-0-c25feb0d2eb3@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This patchset makes it possible to create a new idmapped mount from an
already idmapped mount and to clear idmappings.
// Create a first idmapped mount
struct mount_attr attr = {
.attr_set = MOUNT_ATTR_IDMAP
.userns_fd = fd_userns
};
fd_tree = open_tree(-EBADF, "/", OPEN_TREE_CLONE, &attr, sizeof(attr));
move_mount(fd_tree, "", -EBADF, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
// Create a second idmapped mount from the first idmapped mount
attr.attr_set = MOUNT_ATTR_IDMAP;
attr.userns_fd = fd_userns2;
fd_tree2 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE, &attr, sizeof(attr));
// Create a second non-idmapped mount from the first idmapped mount:
memset(&attr, 0, sizeof(attr));
attr.attr_clr = MOUNT_ATTR_IDMAP;
fd_tree2 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE, &attr, sizeof(attr));
Link: https://lore.kernel.org/r/20250128-work-mnt_idmap-update-v2-v1-5-c25feb0d2eb3@kernel.org
Reviewed-by: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add open_tree_attr() which allow to atomically create a detached mount
tree and set mount options on it. If OPEN_TREE_CLONE is used this will
allow the creation of a detached mount with a new set of mount options
without it ever being exposed to userspace without that set of mount
options applied.
Link: https://lore.kernel.org/r/20250128-work-mnt_idmap-update-v2-v1-3-c25feb0d2eb3@kernel.org
Reviewed-by: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Some of the fields in the statmount() reply can be optional. If the
kernel has nothing to emit in that field, then it doesn't set the flag
in the reply. This presents a problem: There is currently no way to
know what mask flags the kernel supports since you can't always count on
them being in the reply.
Add a new STATMOUNT_SUPPORTED_MASK flag and field that the kernel can
set in the reply. Userland can use this to determine if the fields it
requires from the kernel are supported. This also gives us a way to
deprecate fields in the future, if that should become necessary.
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20250206-statmount-v2-1-6ae70a21c2ab@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This adds the STATMOUNT_MNT_UIDMAP and STATMOUNT_MNT_GIDMAP options.
It allows the retrieval of idmappings via statmount().
Currently it isn't possible to figure out what idmappings are applied to
an idmapped mount. This information is often crucial. Before statmount()
the only realistic options for an interface like this would have been to
add it to /proc/<pid>/fdinfo/<nr> or to expose it in
/proc/<pid>/mountinfo. Both solution would have been pretty ugly and
would've shown information that is of strong interest to some
application but not all. statmount() is perfect for this.
The idmappings applied to an idmapped mount are shown relative to the
caller's user namespace. This is the most useful solution that doesn't
risk leaking information or confuse the caller.
For example, an idmapped mount might have been created with the
following idmappings:
mount --bind -o X-mount.idmap="0:10000:1000 2000:2000:1 3000:3000:1" /srv /opt
Listing the idmappings through statmount() in the same context shows:
mnt_id: 2147485088
mnt_parent_id: 2147484816
fs_type: btrfs
mnt_root: /srv
mnt_point: /opt
mnt_opts: ssd,discard=async,space_cache=v2,subvolid=5,subvol=/
mnt_uidmap[0]: 0 10000 1000
mnt_uidmap[1]: 2000 2000 1
mnt_uidmap[2]: 3000 3000 1
mnt_gidmap[0]: 0 10000 1000
mnt_gidmap[1]: 2000 2000 1
mnt_gidmap[2]: 3000 3000 1
But the idmappings might not always be resolvable in the caller's user
namespace. For example:
unshare --user --map-root
In this case statmount() will skip any mappings that fil to resolve in
the caller's idmapping:
mnt_id: 2147485087
mnt_parent_id: 2147484016
fs_type: btrfs
mnt_root: /srv
mnt_point: /opt
mnt_opts: ssd,discard=async,space_cache=v2,subvolid=5,subvol=/
The caller can differentiate between a mount not being idmapped and a
mount that is idmapped but where all mappings fail to resolve in the
caller's idmapping by check for the STATMOUNT_MNT_{G,U}IDMAP flag being
raised but the number of mappings in ->mnt_{g,u}idmap_num being zero.
Note that statmount() requires that the whole range must be resolvable
in the caller's user namespace. If a subrange fails to map it will still
list the map as not resolvable. This is a practical compromise to avoid
having to find which subranges are resovable and wich aren't.
Idmappings are listed as a string array with each mapping separated by
zero bytes. This allows to retrieve the idmappings and immediately use
them for writing to e.g., /proc/<pid>/{g,u}id_map and it also allow for
simple iteration like:
if (stmnt->mask & STATMOUNT_MNT_UIDMAP) {
const char *idmap = stmnt->str + stmnt->mnt_uidmap;
for (size_t idx = 0; idx < stmnt->mnt_uidmap_nr; idx++) {
printf("mnt_uidmap[%lu]: %s\n", idx, idmap);
idmap += strlen(idmap) + 1;
}
}
Link: https://lore.kernel.org/r/20250204-work-mnt_idmap-statmount-v2-2-007720f39f2e@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
In container workloads idmapped mounts are often used as layers for
overlayfs. Recently I added the ability to specify layers in overlayfs
as file descriptors instead of path names. It should be possible to
simply use the detached mounts directly when specifying layers instead
of having to attach them beforehand. They are discarded after overlayfs
is mounted anyway so it's pointless system calls for userspace and
pointless locking for the kernel.
This just recently come up again in [1]. So enable clone_private_mount()
to use detached mounts directly. Following conditions must be met:
- Provided path must be the root of a detached mount tree.
- Provided path may not create mount namespace loops.
- Provided path must be mounted.
It would be possible to be stricter and require that the caller must
have CAP_SYS_ADMIN in the owning user namespace of the anonymous mount
namespace but since this restriction isn't enforced for move_mount()
there's no point in enforcing it for clone_private_mount().
This contains a folded fix for:
Reported-by: syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=62dfea789a2cedac1298
provided by Lizhi Xu <lizhi.xu@windriver.com> in [2].
Link: https://lore.kernel.org/r/20250207071331.550952-1-lizhi.xu@windriver.com [2]
Link: https://lore.kernel.org/r/fd8f6574-f737-4743-b220-79c815ee1554@mbaynton.com [1]
Link: https://lore.kernel.org/r/20250123-avancieren-erfreuen-3d61f6588fdd@brauner
Tested-by: Mike Baynton <mike@mbaynton.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Prepending security options was made conditional on sb->s_op->show_options,
but security options are independent of sb options.
Fixes: 056d33137b ("fs: prepend statmount.mnt_opts string with security_sb_mnt_opts()")
Fixes: f9af549d1f ("fs: export mount options via statmount()")
Cc: stable@vger.kernel.org # v6.11
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20250129151253.33241-1-mszeredi@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Just like it's normal for unset values to be zero, unset strings should be
empty instead of containing random values.
It seems to be a typical mistake that the mask returned by statmount is not
checked, which can result in various bugs.
With this fix, these bugs are prevented, since it is highly likely that
userspace would just want to turn the missing mask case into an empty
string anyway (most of the recently found cases are of this type).
Link: https://lore.kernel.org/all/CAJfpegsVCPfCn2DpM8iiYSS5DpMsLB8QBUCHecoj6s0Vxf4jzg@mail.gmail.com/
Fixes: 68385d77c0 ("statmount: simplify string option retrieval")
Fixes: 46eae99ef7 ("add statmount(2) syscall")
Cc: stable@vger.kernel.org # v6.8
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20250130121500.113446-1-mszeredi@redhat.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add notifications for attaching and detaching mounts. The following new
event masks are added:
FAN_MNT_ATTACH - Mount was attached
FAN_MNT_DETACH - Mount was detached
If a mount is moved, then the event is reported with (FAN_MNT_ATTACH |
FAN_MNT_DETACH).
These events add an info record of type FAN_EVENT_INFO_TYPE_MNT containing
these fields identifying the affected mounts:
__u64 mnt_id - the ID of the mount (see statmount(2))
FAN_REPORT_MNT must be supplied to fanotify_init() to receive these events
and no other type of event can be received with this report type.
Marks are added with FAN_MARK_MNTNS, which records the mount namespace from
an nsfs file (e.g. /proc/self/ns/mnt).
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20250129165803.72138-3-mszeredi@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add the const qualifier to all the ctl_tables in the tree except for
watchdog_hardlockup_sysctl, memory_allocation_profiling_sysctls,
loadpin_sysctl_table and the ones calling register_net_sysctl (./net,
drivers/inifiniband dirs). These are special cases as they use a
registration function with a non-const qualified ctl_table argument or
modify the arrays before passing them on to the registration function.
Constifying ctl_table structs will prevent the modification of
proc_handler function pointers as the arrays would reside in .rodata.
This is made possible after commit 78eb4ea25c ("sysctl: treewide:
constify the ctl_table argument of proc_handlers") constified all the
proc_handlers.
Created this by running an spatch followed by a sed command:
Spatch:
virtual patch
@
depends on !(file in "net")
disable optional_qualifier
@
identifier table_name != {
watchdog_hardlockup_sysctl,
iwcm_ctl_table,
ucma_ctl_table,
memory_allocation_profiling_sysctls,
loadpin_sysctl_table
};
@@
+ const
struct ctl_table table_name [] = { ... };
sed:
sed --in-place \
-e "s/struct ctl_table .table = &uts_kern/const struct ctl_table *table = \&uts_kern/" \
kernel/utsname_sysctl.c
Reviewed-by: Song Liu <song@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> # for kernel/trace/
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> # SCSI
Reviewed-by: Darrick J. Wong <djwong@kernel.org> # xfs
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Joel Granados <joel.granados@kernel.org>
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Merge tag 'vfs-6.14-rc1.mount.v2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs mount updates from Christian Brauner:
- Add a mountinfo program to demonstrate statmount()/listmount()
Add a new "mountinfo" sample userland program that demonstrates how
to use statmount() and listmount() to get at the same info that
/proc/pid/mountinfo provides
- Remove pointless nospec.h include
- Prepend statmount.mnt_opts string with security_sb_mnt_opts()
Currently these mount options aren't accessible via statmount()
- Add new mount namespaces to mount namespace rbtree outside of the
namespace semaphore
- Lockless mount namespace lookup
Currently we take the read lock when looking for a mount namespace to
list mounts in. We can make this lockless. The simple search case can
just use a sequence counter to detect concurrent changes to the
rbtree
For walking the list of mount namespaces sequentially via nsfs we
keep a separate rcu list as rb_prev() and rb_next() aren't usable
safely with rcu. Currently there is no primitive for retrieving the
previous list member. To do this we need a new deletion primitive
that doesn't poison the prev pointer and a corresponding retrieval
helper
Since creating mount namespaces is a relatively rare event compared
with querying mounts in a foreign mount namespace this is worth it.
Once libmount and systemd pick up this mechanism to list mounts in
foreign mount namespaces this will be used very frequently
- Add extended selftests for lockless mount namespace iteration
- Add a sample program to list all mounts on the system, i.e., in
all mount namespaces
- Improve mount namespace iteration performance
Make finding the last or first mount to start iterating the mount
namespace from an O(1) operation and add selftests for iterating the
mount table starting from the first and last mount
- Use an xarray for the old mount id
While the ida does use the xarray internally we can use it explicitly
which allows us to increment the unique mount id under the xa lock.
This allows us to remove the atomic as we're now allocating both ids
in one go
- Use a shared header for vfs sample programs
- Fix build warnings for new sample program to list all mounts
* tag 'vfs-6.14-rc1.mount.v2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
samples/vfs: fix build warnings
samples/vfs: use shared header
samples/vfs/mountinfo: Use __u64 instead of uint64_t
fs: remove useless lockdep assertion
fs: use xarray for old mount id
selftests: add listmount() iteration tests
fs: cache first and last mount
samples: add test-list-all-mounts
selftests: remove unneeded include
selftests: add tests for mntns iteration
seltests: move nsfs into filesystems subfolder
fs: simplify rwlock to spinlock
fs: lockless mntns lookup for nsfs
rculist: add list_bidir_{del,prev}_rcu()
fs: lockless mntns rbtree lookup
fs: add mount namespace to rbtree late
fs: prepend statmount.mnt_opts string with security_sb_mnt_opts()
mount: remove inlude/nospec.h include
samples: add a mountinfo program to demonstrate statmount()/listmount()
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Merge tag 'vfs-6.14-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull pidfs updates from Christian Brauner:
- Rework inode number allocation
Recently we received a patchset that aims to enable file handle
encoding and decoding via name_to_handle_at(2) and
open_by_handle_at(2).
A crucical step in the patch series is how to go from inode number to
struct pid without leaking information into unprivileged contexts.
The issue is that in order to find a struct pid the pid number in the
initial pid namespace must be encoded into the file handle via
name_to_handle_at(2).
This can be used by containers using a separate pid namespace to
learn what the pid number of a given process in the initial pid
namespace is. While this is a weak information leak it could be used
in various exploits and in general is an ugly wart in the design.
To solve this problem a new way is needed to lookup a struct pid
based on the inode number allocated for that struct pid. The other
part is to remove the custom inode number allocation on 32bit systems
that is also an ugly wart that should go away.
Allocate unique identifiers for struct pid by simply incrementing a
64 bit counter and insert each struct pid into the rbtree so it can
be looked up to decode file handles avoiding to leak actual pids
across pid namespaces in file handles.
On both 64 bit and 32 bit the same 64 bit identifier is used to
lookup struct pid in the rbtree. On 64 bit the unique identifier for
struct pid simply becomes the inode number. Comparing two pidfds
continues to be as simple as comparing inode numbers.
On 32 bit the 64 bit number assigned to struct pid is split into two
32 bit numbers. The lower 32 bits are used as the inode number and
the upper 32 bits are used as the inode generation number. Whenever a
wraparound happens on 32 bit the 64 bit number will be incremented by
2 so inode numbering starts at 2 again.
When a wraparound happens on 32 bit multiple pidfds with the same
inode number are likely to exist. This isn't a problem since before
pidfs pidfds used the anonymous inode meaning all pidfds had the same
inode number. On 32 bit sserspace can thus reconstruct the 64 bit
identifier by retrieving both the inode number and the inode
generation number to compare, or use file handles. This gives the
same guarantees on both 32 bit and 64 bit.
- Implement file handle support
This is based on custom export operation methods which allows pidfs
to implement permission checking and opening of pidfs file handles
cleanly without hacking around in the core file handle code too much.
- Support bind-mounts
Allow bind-mounting pidfds. Similar to nsfs let's allow bind-mounts
for pidfds. This allows pidfds to be safely recovered and checked for
process recycling.
Instead of checking d_ops for both nsfs and pidfs we could in a
follow-up patch add a flag argument to struct dentry_operations that
functions similar to file_operations->fop_flags.
* tag 'vfs-6.14-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
selftests: add pidfd bind-mount tests
pidfs: allow bind-mounts
pidfs: lookup pid through rbtree
selftests/pidfd: add pidfs file handle selftests
pidfs: check for valid ioctl commands
pidfs: implement file handle support
exportfs: add permission method
fhandle: pull CAP_DAC_READ_SEARCH check into may_decode_fh()
exportfs: add open method
fhandle: simplify error handling
pseudofs: add support for export_ops
pidfs: support FS_IOC_GETVERSION
pidfs: remove 32bit inode number handling
pidfs: rework inode number allocation
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Merge tag 'vfs-6.14-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull misc vfs updates from Christian Brauner:
"Features:
- Support caching symlink lengths in inodes
The size is stored in a new union utilizing the same space as
i_devices, thus avoiding growing the struct or taking up any more
space
When utilized it dodges strlen() in vfs_readlink(), giving about
1.5% speed up when issuing readlink on /initrd.img on ext4
- Add RWF_DONTCACHE iocb and FOP_DONTCACHE file_operations flag
If a file system supports uncached buffered IO, it may set
FOP_DONTCACHE and enable support for RWF_DONTCACHE.
If RWF_DONTCACHE is attempted without the file system supporting
it, it'll get errored with -EOPNOTSUPP
- Enable VBOXGUEST and VBOXSF_FS on ARM64
Now that VirtualBox is able to run as a host on arm64 (e.g. the
Apple M3 processors) we can enable VBOXSF_FS (and in turn
VBOXGUEST) for this architecture.
Tested with various runs of bonnie++ and dbench on an Apple MacBook
Pro with the latest Virtualbox 7.1.4 r165100 installed
Cleanups:
- Delay sysctl_nr_open check in expand_files()
- Use kernel-doc includes in fiemap docbook
- Use page->private instead of page->index in watch_queue
- Use a consume fence in mnt_idmap() as it's heavily used in
link_path_walk()
- Replace magic number 7 with ARRAY_SIZE() in fc_log
- Sort out a stale comment about races between fd alloc and dup2()
- Fix return type of do_mount() from long to int
- Various cosmetic cleanups for the lockref code
Fixes:
- Annotate spinning as unlikely() in __read_seqcount_begin
The annotation already used to be there, but got lost in commit
52ac39e5db ("seqlock: seqcount_t: Implement all read APIs as
statement expressions")
- Fix proc_handler for sysctl_nr_open
- Flush delayed work in delayed fput()
- Fix grammar and spelling in propagate_umount()
- Fix ESP not readable during coredump
In /proc/PID/stat, there is the kstkesp field which is the stack
pointer of a thread. While the thread is active, this field reads
zero. But during a coredump, it should have a valid value
However, at the moment, kstkesp is zero even during coredump
- Don't wake up the writer if the pipe is still full
- Fix unbalanced user_access_end() in select code"
* tag 'vfs-6.14-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (28 commits)
gfs2: use lockref_init for qd_lockref
erofs: use lockref_init for pcl->lockref
dcache: use lockref_init for d_lockref
lockref: add a lockref_init helper
lockref: drop superfluous externs
lockref: use bool for false/true returns
lockref: improve the lockref_get_not_zero description
lockref: remove lockref_put_not_zero
fs: Fix return type of do_mount() from long to int
select: Fix unbalanced user_access_end()
vbox: Enable VBOXGUEST and VBOXSF_FS on ARM64
pipe_read: don't wake up the writer if the pipe is still full
selftests: coredump: Add stackdump test
fs/proc: do_task_stat: Fix ESP not readable during coredump
fs: add RWF_DONTCACHE iocb and FOP_DONTCACHE file_operations flag
fs: sort out a stale comment about races between fd alloc and dup2
fs: Fix grammar and spelling in propagate_umount()
fs: fc_log replace magic number 7 with ARRAY_SIZE()
fs: use a consume fence in mnt_idmap()
file: flush delayed work in delayed fput()
...
Fix the return type of do_mount() function from long to int to match its ac
tual behavior. The function only returns int values, and all callers, inclu
ding those in fs/namespace.c and arch/alpha/kernel/osf_sys.c, already treat
the return value as int. This change improves type consistency across the
filesystem code and aligns the function signature with its existing impleme
ntation and usage.
Signed-off-by: Sentaro Onizuka <sentaro@amazon.com>
Link: https://lore.kernel.org/r/20250113151400.55512-1-sentaro@amazon.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'vfs-6.14-rc7.mount.fixes'
Bring in the fix for the mount namespace rbtree. It is used as the base
for the vfs mount work for this cycle and so shouldn't be applied
directly.
Signed-off-by: Christian Brauner <brauner@kernel.org>
While the ida does use the xarray internally we can use it explicitly
which allows us to increment the unique mount id under the xa lock.
This allows us to remove the atomic as we're now allocating both ids in
one go.
Link: https://lore.kernel.org/r/20241217-erhielten-regung-44bb1604ca8f@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>
We already made the rbtree lookup lockless for the simple lookup case.
However, walking the list of mount namespaces via nsfs still happens
with taking the read lock blocking concurrent additions of new mount
namespaces pointlessly. Plus, such additions are rare anyway so allow
lockless lookup of the previous and next mount namespace by keeping a
separate list. This also allows to make some things simpler in the code.
Link: https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-5-6e3cdaf9b280@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Currently we use a read-write lock but for the simple search case we can
make this lockless. Creating a new mount namespace is a rather rare
event compared with querying mounts in a foreign mount namespace. Once
this is picked up by e.g., systemd to list mounts in another mount in
it's isolated services or in containers this will be used a lot so this
seems worthwhile doing.
Link: https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-3-6e3cdaf9b280@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Al Viro
Jan Stancek
Christian Brauner
Gustavo A. R. Silva
Linus Torvalds
Trond Myklebust
Arnd Bergmann
Jeff Layton
Miklos Szeredi
Joel Granados
Sentaro Onizuka