This is a note to let you know that I've just added the patch titled net/x25: Fix null-ptr-deref caused by x25_disconnect to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-x25-fix-null-ptr-deref-caused-by-x25_disconnect.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit a79aeab25dbf90920bb172cb9de97140608f5a8c Author: Duoming Zhou <duoming@xxxxxxxxxx> Date: Sat Mar 26 18:43:46 2022 +0800 net/x25: Fix null-ptr-deref caused by x25_disconnect [ Upstream commit 7781607938c8371d4c2b243527430241c62e39c2 ] When the link layer is terminating, x25->neighbour will be set to NULL in x25_disconnect(). As a result, it could cause null-ptr-deref bugs in x25_sendmsg(),x25_recvmsg() and x25_connect(). One of the bugs is shown below. (Thread 1) | (Thread 2) x25_link_terminated() | x25_recvmsg() x25_kill_by_neigh() | ... x25_disconnect() | lock_sock(sk) ... | ... x25->neighbour = NULL //(1) | ... | x25->neighbour->extended //(2) The code sets NULL to x25->neighbour in position (1) and dereferences x25->neighbour in position (2), which could cause null-ptr-deref bug. This patch adds lock_sock() in x25_kill_by_neigh() in order to synchronize with x25_sendmsg(), x25_recvmsg() and x25_connect(). What`s more, the sock held by lock_sock() is not NULL, because it is extracted from x25_list and uses x25_list_lock to synchronize. Fixes: 4becb7ee5b3d ("net/x25: Fix x25_neigh refcnt leak when x25 disconnect") Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx> Reviewed-by: Lin Ma <linma@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c index 3583354a7d7f..3a171828638b 100644 --- a/net/x25/af_x25.c +++ b/net/x25/af_x25.c @@ -1765,10 +1765,15 @@ void x25_kill_by_neigh(struct x25_neigh *nb) write_lock_bh(&x25_list_lock); - sk_for_each(s, &x25_list) - if (x25_sk(s)->neighbour == nb) + sk_for_each(s, &x25_list) { + if (x25_sk(s)->neighbour == nb) { + write_unlock_bh(&x25_list_lock); + lock_sock(s); x25_disconnect(s, ENETUNREACH, 0, 0); - + release_sock(s); + write_lock_bh(&x25_list_lock); + } + } write_unlock_bh(&x25_list_lock); /* Remove any related forwards */