[PATCH 3.2 198/199] sctp: avoid BUG_ON on sctp_wait_for_sndbuf

[Ben Hutchings]

3.2.87-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>

commit 2dcab598484185dea7ec22219c76dcdd59e3cb90 upstream.

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 <alex.popov@xxxxxxxxx>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
Reviewed-by: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/sctp/socket.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -6492,7 +6492,8 @@ static int sctp_wait_for_sndbuf(struct s
 		 */
 		sctp_release_sock(sk);
 		current_timeo = schedule_timeout(current_timeo);
-		BUG_ON(sk != asoc->base.sk);
+		if (sk != asoc->base.sk)
+			goto do_error;
 		sctp_lock_sock(sk);
 
 		*timeo_p = current_timeo;