From: Stefano Garzarella <[email protected]>
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 687aa0c5581b ("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: [email protected]
Tested-by: [email protected]
Fixes: 687aa0c5581b ("vsock: Fix transport_* TOCTOU")
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Stefano Garzarella <[email protected]>
---
net/vmw_vsock/af_vsock.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 4c2db6cca557..76763247a377 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -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) {
- ret = 0;
- goto err;
- }
+ 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)) {
--
2.51.0
