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vsock: fix lock inversion in vsock_assign_transport() 

Syzbot reported a potential lock inversion deadlock between
vsock_register_mutex and sk_lock-AF_VSOCK when vsock_linger() is called.

The issue was introduced by commit 687aa0c558 ("vsock: Fix
transport_* TOCTOU") which added vsock_register_mutex locking in
vsock_assign_transport() around the transport->release() call, that can
call vsock_linger(). vsock_assign_transport() can be called with sk_lock
held. vsock_linger() calls sk_wait_event() that temporarily releases and
re-acquires sk_lock. During this window, if another thread hold
vsock_register_mutex while trying to acquire sk_lock, a circular
dependency is created.

Fix this by releasing vsock_register_mutex before calling
transport->release() and vsock_deassign_transport(). This is safe
because we don't need to hold vsock_register_mutex while releasing the
old transport, and we ensure the new transport won't disappear by
obtaining a module reference first via try_module_get().

Reported-by: syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com
Tested-by: syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com
Fixes: 687aa0c558 ("vsock: Fix transport_* TOCTOU")
Cc: mhal@rbox.co
Cc: stable@vger.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20251021121718.137668-1-sgarzare@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Stefano Garzarella 2025-10-21 14:17:18 +02:00 committed by Paolo Abeni
parent df890ceeb2
commit f7c877e753
1 changed files with 19 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
net/vmw_vsock/af_vsock.c
View File

@ -487,12 +487,26 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
goto err; goto err;
} }
if (vsk->transport) { if (vsk->transport && vsk->transport == new_transport) {
if (vsk->transport == new_transport) { ret = 0;
ret = 0; goto err;
goto err; }
}
/* We increase the module refcnt to prevent the transport unloading
* while there are open sockets assigned to it.
*/
if (!new_transport || !try_module_get(new_transport->module)) {
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 (vsk->transport) {
/* 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
* have already held the sock lock. In the other cases, this * have already held the sock lock. In the other cases, this
@ -512,20 +526,6 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
vsk->peer_shutdown = 0; vsk->peer_shutdown = 0;
} }
/* We increase the module refcnt to prevent the transport unloading
* while there are open sockets assigned to it.
*/
if (!new_transport || !try_module_get(new_transport->module)) {
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 ||
!new_transport->seqpacket_allow(remote_cid)) { !new_transport->seqpacket_allow(remote_cid)) {