Commit f7c877e7 authored by Stefano Garzarella's avatar Stefano Garzarella Committed by Paolo Abeni
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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 687aa0c5 ("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: default avatar <syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com>
Tested-by: default avatar <syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com>
Fixes: 687aa0c5 ("vsock: Fix transport_* TOCTOU")
Cc: mhal@rbox.co
Cc: stable@vger.kernel.org
Signed-off-by: default avatarStefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20251021121718.137668-1-sgarzare@redhat.com


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent df890cee

net/vmw_vsock/af_vsock.c

+19 −19
Original line number Diff line number Diff line
@@ -487,12 +487,26 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) 
		goto err;

	}



	if (vsk->transport) {

		if (vsk->transport == new_transport) {

	if (vsk->transport && vsk->transport == new_transport) {

		ret = 0;

		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.

		 * This path can only be taken during vsock_connect(), where we

		 * 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;

	}



	/* 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 (!new_transport->seqpacket_allow ||

		    !new_transport->seqpacket_allow(remote_cid)) {