Patch "inet: fix races with reqsk timers" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

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

    inet: fix races with reqsk timers

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-races-with-reqsk-timers.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 <stable@vger.kernel.org> know about it.


>From foo@baz Sat Sep 26 11:13:07 PDT 2015
From: Eric Dumazet <edumazet@google.com>
Date: Mon, 10 Aug 2015 09:09:13 -0700
Subject: inet: fix races with reqsk timers

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 2235f2ac75fd2501c251b0b699a9632e80239a6d ]

reqsk_queue_destroy() and reqsk_queue_unlink() should use
del_timer_sync() instead of del_timer() before calling reqsk_put(),
otherwise we could free a req still used by another cpu.

But before doing so, reqsk_queue_destroy() must release syn_wait_lock
spinlock or risk a dead lock, as reqsk_timer_handler() might
need to take this same spinlock from reqsk_queue_unlink() (called from
inet_csk_reqsk_queue_drop())

Fixes: fa76ce7328b2 ("inet: get rid of central tcp/dccp listener timer")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/request_sock.c         |    8 +++++++-
 net/ipv4/inet_connection_sock.c |    2 +-
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/net/core/request_sock.c
+++ b/net/core/request_sock.c
@@ -103,10 +103,16 @@ void reqsk_queue_destroy(struct request_
 			spin_lock_bh(&queue->syn_wait_lock);
 			while ((req = lopt->syn_table[i]) != NULL) {
 				lopt->syn_table[i] = req->dl_next;
+				/* Because of following del_timer_sync(),
+				 * we must release the spinlock here
+				 * or risk a dead lock.
+				 */
+				spin_unlock_bh(&queue->syn_wait_lock);
 				atomic_inc(&lopt->qlen_dec);
-				if (del_timer(&req->rsk_timer))
+				if (del_timer_sync(&req->rsk_timer))
 					reqsk_put(req);
 				reqsk_put(req);
+				spin_lock_bh(&queue->syn_wait_lock);
 			}
 			spin_unlock_bh(&queue->syn_wait_lock);
 		}
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -584,7 +584,7 @@ static bool reqsk_queue_unlink(struct re
 	}
 
 	spin_unlock(&queue->syn_wait_lock);
-	if (del_timer(&req->rsk_timer))
+	if (del_timer_sync(&req->rsk_timer))
 		reqsk_put(req);
 	return found;
 }


Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.1/udp-fix-dst-races-with-multicast-early-demux.patch
queue-4.1/fq_codel-fix-a-use-after-free.patch
queue-4.1/inet-fix-possible-request-socket-leak.patch
queue-4.1/ipv6-lock-socket-in-ip6_datagram_connect.patch
queue-4.1/net-fix-skb-csum-races-when-peeking.patch
queue-4.1/inet-fix-races-with-reqsk-timers.patch
queue-4.1/net-graceful-exit-from-netif_alloc_netdev_queues.patch
queue-4.1/bridge-fix-potential-crash-in-__netdev_pick_tx.patch
queue-4.1/inet-frags-fix-defragmented-packet-s-ip-header-for-af_packet.patch