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tcp/dccp: fix timewait races in timer handling

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When creating a timewait socket, we need to arm the timer before
allowing other cpus to find it. The signal allowing cpus to find
the socket is setting tw_refcnt to non zero value.

As we set tw_refcnt in __inet_twsk_hashdance(), we therefore need to
call inet_twsk_schedule() first.

This also means we need to remove tw_refcnt changes from
inet_twsk_schedule() and let the caller handle it.

Note that because we use mod_timer_pinned(), we have the guarantee
the timer wont expire before we set tw_refcnt as we run in BH context.

To make things more readable I introduced inet_twsk_reschedule() helper.

When rearming the timer, we can use mod_timer_pending() to make sure
we do not rearm a canceled timer.

Note: This bug can possibly trigger if packets of a flow can hit
multiple cpus. This does not normally happen, unless flow steering
is broken somehow. This explains this bug was spotted ~5 months after
its introduction.

A similar fix is needed for SYN_RECV sockets in reqsk_queue_hash_req(),
but will be provided in a separate patch for proper tracking.

Fixes: 789f558cfb ("tcp/dccp: get rid of central timewait timer")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Ying Cai <ycai@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-09-19 09:08:34 -07:00 committed by David S. Miller
parent 4c5d283acc
commit ed2e923945
4 changed files with 31 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
include/net/inet_timewait_sock.h
View File

@ -110,7 +110,19 @@ struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
struct inet_hashinfo *hashinfo);
void inet_twsk_schedule(struct inet_timewait_sock *tw, const int timeo);
void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo,
bool rearm);
static void inline inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo)
{
__inet_twsk_schedule(tw, timeo, false);
}
static void inline inet_twsk_reschedule(struct inet_timewait_sock *tw, int timeo)
{
__inet_twsk_schedule(tw, timeo, true);
}
void inet_twsk_deschedule_put(struct inet_timewait_sock *tw);
void inet_twsk_purge(struct inet_hashinfo *hashinfo,

4
net/dccp/minisocks.c
View File

@ -48,8 +48,6 @@ void dccp_time_wait(struct sock *sk, int state, int timeo)
tw->tw_ipv6only = sk->sk_ipv6only;
}
#endif
/* Linkage updates. */
__inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
/* Get the TIME_WAIT timeout firing. */
if (timeo < rto)
@ -60,6 +58,8 @@ void dccp_time_wait(struct sock *sk, int state, int timeo)
timeo = DCCP_TIMEWAIT_LEN;
inet_twsk_schedule(tw, timeo);
/* Linkage updates. */
__inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
inet_twsk_put(tw);
} else {
/* Sorry, if we're out of memory, just CLOSE this

16
net/ipv4/inet_timewait_sock.c
View File

@ -123,13 +123,15 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
/*
* Step 2: Hash TW into tcp ehash chain.
* Notes :
* - tw_refcnt is set to 3 because :
* - tw_refcnt is set to 4 because :
* - We have one reference from bhash chain.
* - We have one reference from ehash chain.
* - We have one reference from timer.
* - One reference for ourself (our caller will release it).
* We can use atomic_set() because prior spin_lock()/spin_unlock()
* committed into memory all tw fields.
*/
atomic_set(&tw->tw_refcnt, 1 + 1 + 1);
atomic_set(&tw->tw_refcnt, 4);
inet_twsk_add_node_rcu(tw, &ehead->chain);
/* Step 3: Remove SK from hash chain */
@ -217,7 +219,7 @@ void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
}
EXPORT_SYMBOL(inet_twsk_deschedule_put);
void inet_twsk_schedule(struct inet_timewait_sock *tw, const int timeo)
void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
{
/* timeout := RTO * 3.5
*
@ -245,12 +247,14 @@ void inet_twsk_schedule(struct inet_timewait_sock *tw, const int timeo)
*/
tw->tw_kill = timeo <= 4*HZ;
if (!mod_timer_pinned(&tw->tw_timer, jiffies + timeo)) {
atomic_inc(&tw->tw_refcnt);
if (!rearm) {
BUG_ON(mod_timer_pinned(&tw->tw_timer, jiffies + timeo));
atomic_inc(&tw->tw_dr->tw_count);
} else {
mod_timer_pending(&tw->tw_timer, jiffies + timeo);
}
}
EXPORT_SYMBOL_GPL(inet_twsk_schedule);
EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
void inet_twsk_purge(struct inet_hashinfo *hashinfo,
struct inet_timewait_death_row *twdr, int family)

13
net/ipv4/tcp_minisocks.c
View File

@ -162,9 +162,9 @@ kill_with_rst:
if (tcp_death_row.sysctl_tw_recycle &&
tcptw->tw_ts_recent_stamp &&
tcp_tw_remember_stamp(tw))
inet_twsk_schedule(tw, tw->tw_timeout);
inet_twsk_reschedule(tw, tw->tw_timeout);
else
inet_twsk_schedule(tw, TCP_TIMEWAIT_LEN);
inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
return TCP_TW_ACK;
}
@ -201,7 +201,7 @@ kill:
return TCP_TW_SUCCESS;
}
}
inet_twsk_schedule(tw, TCP_TIMEWAIT_LEN);
inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
if (tmp_opt.saw_tstamp) {
tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
@ -251,7 +251,7 @@ kill:
* Do not reschedule in the last case.
*/
if (paws_reject || th->ack)
inet_twsk_schedule(tw, TCP_TIMEWAIT_LEN);
inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
return tcp_timewait_check_oow_rate_limit(
tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
@ -322,9 +322,6 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
} while (0);
#endif
/* Linkage updates. */
__inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
/* Get the TIME_WAIT timeout firing. */
if (timeo < rto)
timeo = rto;
@ -338,6 +335,8 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
}
inet_twsk_schedule(tw, timeo);
/* Linkage updates. */
__inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
inet_twsk_put(tw);
} else {
/* Sorry, if we're out of memory, just CLOSE this