tcp/dccp: block bh before arming time_wait timer

[ 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>

diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index abd07a443219853b022bef41cb072e90ff8f07f0..178bb9833311f83205317b07fe64cb2e45a9f734 100644 (file)
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -57,10 +57,16 @@ void dccp_time_wait(struct sock *sk, int state, int timeo)
                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

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 188a6f31356db0d0b7825aa476888467f7c0dfd8..420fecbb98fe7edc3a215455d603997c95b7ced3 100644 (file)
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -312,10 +312,16 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
                if (state == TCP_TIME_WAIT)
                        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