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vsock: Fix transport_* TOCTOU 

Transport assignment may race with module unload. Protect new_transport
from becoming a stale pointer.

This also takes care of an insecure call in vsock_use_local_transport();
add a lockdep assert.

BUG: unable to handle page fault for address: fffffbfff8056000
Oops: Oops: 0000 [#1] SMP KASAN
RIP: 0010:vsock_assign_transport+0x366/0x600
Call Trace:
 vsock_connect+0x59c/0xc40
 __sys_connect+0xe8/0x100
 __x64_sys_connect+0x6e/0xc0
 do_syscall_64+0x92/0x1c0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

Fixes: c0cfa2d8a7 ("vsock: add multi-transports support")
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250703-vsock-transports-toctou-v4-2-98f0eb530747@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Michal Luczaj 2025-07-03 17:18:19 +02:00 committed by Jakub Kicinski
parent 209fd72083
commit 687aa0c558
1 changed files with 23 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
net/vmw_vsock/af_vsock.c
View File

@ -407,6 +407,8 @@ EXPORT_SYMBOL_GPL(vsock_enqueue_accept);
static bool vsock_use_local_transport(unsigned int remote_cid) static bool vsock_use_local_transport(unsigned int remote_cid)
{ {
lockdep_assert_held(&vsock_register_mutex);
if (!transport_local) if (!transport_local)
return false; return false;
@ -464,6 +466,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
remote_flags = vsk->remote_addr.svm_flags; remote_flags = vsk->remote_addr.svm_flags;
mutex_lock(&vsock_register_mutex);
switch (sk->sk_type) { switch (sk->sk_type) {
case SOCK_DGRAM: case SOCK_DGRAM:
new_transport = transport_dgram; new_transport = transport_dgram;
@ -479,12 +483,15 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
new_transport = transport_h2g; new_transport = transport_h2g;
break; break;
default: default:
return -ESOCKTNOSUPPORT; ret = -ESOCKTNOSUPPORT;
goto err;
} }
if (vsk->transport) { if (vsk->transport) {
if (vsk->transport == new_transport) if (vsk->transport == new_transport) {
return 0; ret = 0;
goto err;
}
/* transport->release() must be called with sock lock acquired. /* transport->release() must be called with sock lock acquired.
* This path can only be taken during vsock_connect(), where we * This path can only be taken during vsock_connect(), where we
@ -508,8 +515,16 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
/* We increase the module refcnt to prevent the transport unloading /* We increase the module refcnt to prevent the transport unloading
* while there are open sockets assigned to it. * while there are open sockets assigned to it.
*/ */
if (!new_transport || !try_module_get(new_transport->module)) if (!new_transport || !try_module_get(new_transport->module)) {
return -ENODEV; ret = -ENODEV;
goto err;
}
/* It's safe to release the mutex after a successful try_module_get().
* Whichever transport `new_transport` points at, it won't go away until
* the last module_put() below or in vsock_deassign_transport().
*/
mutex_unlock(&vsock_register_mutex);
if (sk->sk_type == SOCK_SEQPACKET) { if (sk->sk_type == SOCK_SEQPACKET) {
if (!new_transport->seqpacket_allow || if (!new_transport->seqpacket_allow ||
@ -528,6 +543,9 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
vsk->transport = new_transport; vsk->transport = new_transport;
return 0; return 0;
err:
mutex_unlock(&vsock_register_mutex);
return ret;
} }
EXPORT_SYMBOL_GPL(vsock_assign_transport); EXPORT_SYMBOL_GPL(vsock_assign_transport);