tcp, ulp: remove socket lock assertion on ULP cleanup

Eric reported that syzkaller triggered a splat in tcp_cleanup_ulp()
where assertion sock_owned_by_me() failed. This happened through
inet_csk_prepare_forced_close() first releasing the socket lock,
then calling into tcp_done(newsk) which is called after the
inet_csk_prepare_forced_close() and therefore without the socket
lock held. The sock_owned_by_me() assertion can generally be
removed as the only place where tcp_cleanup_ulp() is called from
now is out of inet_csk_destroy_sock() -> sk->sk_prot->destroy()
where socket is in dead state and unreachable. Therefore, add a
comment why the check is not needed instead.

Fixes: 8b9088f806e1 ("tcp, ulp: enforce sock_owned_by_me upon ulp init and cleanup")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_ulp.c b/net/ipv4/tcp_ulp.c
index a9162aa11af9ae79e258de5c0fed2becfb24474f..95df7f7f6328b86e2d24cc62695e598f73e8a96d 100644 (file)
--- a/net/ipv4/tcp_ulp.c
+++ b/net/ipv4/tcp_ulp.c
@@ -99,8 +99,10 @@ void tcp_cleanup_ulp(struct sock *sk)
 {
        struct inet_connection_sock *icsk = inet_csk(sk);
 
-       sock_owned_by_me(sk);
-
+       /* No sock_owned_by_me() check here as at the time the
+        * stack calls this function, the socket is dead and
+        * about to be destroyed.
+        */
        if (!icsk->icsk_ulp_ops)
                return;