From f88649721268999bdff09777847080a52004f691 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 24 Jun 2014 10:05:11 -0700 Subject: ipv4: fix dst race in sk_dst_get() When IP route cache had been removed in linux-3.6, we broke assumption that dst entries were all freed after rcu grace period. DST_NOCACHE dst were supposed to be freed from dst_release(). But it appears we want to keep such dst around, either in UDP sockets or tunnels. In sk_dst_get() we need to make sure dst refcount is not 0 before incrementing it, or else we might end up freeing a dst twice. DST_NOCACHE set on a dst does not mean this dst can not be attached to a socket or a tunnel. Then, before actual freeing, we need to observe a rcu grace period to make sure all other cpus can catch the fact the dst is no longer usable. Signed-off-by: Eric Dumazet Reported-by: Dormando Signed-off-by: David S. Miller --- include/net/sock.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/net/sock.h b/include/net/sock.h index 07b7fcd60d80..173cae485de1 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1730,8 +1730,8 @@ sk_dst_get(struct sock *sk) rcu_read_lock(); dst = rcu_dereference(sk->sk_dst_cache); - if (dst) - dst_hold(dst); + if (dst && !atomic_inc_not_zero(&dst->__refcnt)) + dst = NULL; rcu_read_unlock(); return dst; } -- cgit v1.2.3