Patch "inet: fix race in reqsk_queue_unlink()" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

inet: fix race in reqsk_queue_unlink()

to the 4.1-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:
inet-fix-race-in-reqsk_queue_unlink.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Thu, 1 Oct 2015 05:39:26 -0700
Subject: inet: fix race in reqsk_queue_unlink()

From: Eric Dumazet <[email protected]>

[ Upstream commit 2306c704ce280c97a60d1f45333b822b40281dea ]

reqsk_timer_handler() tests if icsk_accept_queue.listen_opt is NULL at its beginning.

By the time it calls inet_csk_reqsk_queue_drop() and reqsk_queue_unlink(), listener might have been closed and inet_csk_listen_stop() had called reqsk_queue_yank_acceptq() which sets icsk_accept_queue.listen_opt to NULL

We therefore need to correctly check listen_opt being NULL after holding syn_wait_lock for proper synchronization.

---
 net/ipv4/inet_connection_sock.c |   19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

@@ -568,21 +568,22 @@ EXPORT_SYMBOL(inet_rtx_syn_ack);
 static bool reqsk_queue_unlink(struct request_sock_queue *queue,
 			       struct request_sock *req)
 {
-	struct listen_sock *lopt = queue->listen_opt;
 	struct request_sock **prev;
+	struct listen_sock *lopt;
 	bool found = false;
 
 	spin_lock(&queue->syn_wait_lock);
-
-	for (prev = &lopt->syn_table[req->rsk_hash]; *prev != NULL;
-	     prev = &(*prev)->dl_next) {
-		if (*prev == req) {
-			*prev = req->dl_next;
-			found = true;
-			break;
+	lopt = queue->listen_opt;
+	if (lopt) {
+		for (prev = &lopt->syn_table[req->rsk_hash]; *prev != NULL;
+		     prev = &(*prev)->dl_next) {
+			if (*prev == req) {
+				*prev = req->dl_next;
+				found = true;
+				break;
+			}
 		}
 	}
-
 	spin_unlock(&queue->syn_wait_lock);
 	if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer))
 		reqsk_put(req);

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/inet-fix-races-in-reqsk_queue_hash_req.patch queue-4.1/net-add-pfmemalloc-check-in-sk_add_backlog.patch queue-4.1/inet-fix-race-in-reqsk_queue_unlink.patch queue-4.1/net-unix-fix-logic-about-sk_peek_offset.patch queue-4.1/act_mirred-clear-sender-cpu-before-sending-to-tx.patch