Patch "tcp/dccp: block bh before arming time_wait timer" has been added to the 4.9-stable tree

Patch "tcp/dccp: block bh before arming time_wait timer" has been added to the 4.9-stable tree

[gregkh]

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

    tcp/dccp: block bh before arming time_wait timer

to the 4.9-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:
     tcp-dccp-block-bh-before-arming-time_wait-timer.patch
and it can be found in the queue-4.9 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 Thu Dec 14 11:45:58 CET 2017
From: Eric Dumazet <edumazet@google.com>
Date: Fri, 1 Dec 2017 10:06:56 -0800
Subject: tcp/dccp: block bh before arming time_wait timer

From: Eric Dumazet <edumazet@google.com>


[ Upstream commit cfac7f836a715b91f08c851df915d401a4d52783 ]

Maciej Żenczykowski reported some panics in tcp_twsk_destructor()
that might be caused by the following bug.

timewait timer is pinned to the cpu, because we want to transition
timwewait refcount from 0 to 4 in one go, once everything has been
initialized.

At the time commit ed2e92394589 ("tcp/dccp: fix timewait races in timer
handling") was merged, TCP was always running from BH habdler.

After commit 5413d1babe8f ("net: do not block BH while processing
socket backlog") we definitely can run tcp_time_wait() from process
context.

We need to block BH in the critical section so that the pinned timer
has still its purpose.

This bug is more likely to happen under stress and when very small RTO
are used in datacenter flows.

Fixes: 5413d1babe8f ("net: do not block BH while processing socket backlog")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Maciej Żenczykowski <maze@google.com>
Acked-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/dccp/minisocks.c     |    6 ++++++
 net/ipv4/tcp_minisocks.c |    6 ++++++
 2 files changed, 12 insertions(+)

--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -57,10 +57,16 @@ void dccp_time_wait(struct sock *sk, int
 		if (state == DCCP_TIME_WAIT)
 			timeo = DCCP_TIMEWAIT_LEN;
 
+		/* tw_timer is pinned, so we need to make sure BH are disabled
+		 * in following section, otherwise timer handler could run before
+		 * we complete the initialization.
+		 */
+		local_bh_disable();
 		inet_twsk_schedule(tw, timeo);
 		/* Linkage updates. */
 		__inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
 		inet_twsk_put(tw);
+		local_bh_enable();
 	} else {
 		/* Sorry, if we're out of memory, just CLOSE this
 		 * socket up.  We've got bigger problems than
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -328,10 +328,16 @@ void tcp_time_wait(struct sock *sk, int
 				timeo = TCP_TIMEWAIT_LEN;
 		}
 
+		/* tw_timer is pinned, so we need to make sure BH are disabled
+		 * in following section, otherwise timer handler could run before
+		 * we complete the initialization.
+		 */
+		local_bh_disable();
 		inet_twsk_schedule(tw, timeo);
 		/* Linkage updates. */
 		__inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
 		inet_twsk_put(tw);
+		local_bh_enable();
 	} else {
 		/* Sorry, if we're out of memory, just CLOSE this
 		 * socket up.  We've got bigger problems than


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

queue-4.9/net-packet-fix-a-race-in-packet_bind-and-packet_notifier.patch
queue-4.9/packet-fix-crash-in-fanout_demux_rollover.patch
queue-4.9/net-remove-hlist_nulls_add_tail_rcu.patch
queue-4.9/tcp-dccp-block-bh-before-arming-time_wait-timer.patch