[PATCH net] sctp: avoid BUG_ON on sctp_wait_for_sndbuf

Alexander Popov reported that an application may trigger a BUG_ON in
sctp_wait_for_sndbuf if the socket tx buffer is full, a thread is
waiting on it to queue more data and meanwhile another thread peels off
the association being used by the first thread.

This patch replaces the BUG_ON call with a proper error handling. It
will return -EPIPE to the original sendmsg call, similarly to what would
have been done if the association wasn't found in the first place.

Acked-by: Alexander Popov <redacted>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
---
Please consider this to -stable. Thanks

 net/sctp/socket.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 37eeab7899fc235a56bd2f4ccdb3e6c338a8d48e..e214d2e7e9a30c02847daf354668c42eeaffd0d6 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c

@@ -7426,7 +7426,8 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p,
 		 */
 		release_sock(sk);
 		current_timeo = schedule_timeout(current_timeo);
-		BUG_ON(sk != asoc->base.sk);
+		if (sk != asoc->base.sk)
+			goto do_error;
 		lock_sock(sk);
 
 		*timeo_p = current_timeo;

-- 
2.9.3