From f88649721268999bdff09777847080a52004f691 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 24 Jun 2014 10:05:11 -0700 Subject: [PATCH] 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 ++-- net/core/dst.c | 16 +++++++++++----- net/ipv4/ip_tunnel.c | 14 +++++--------- 3 files changed, 18 insertions(+), 16 deletions(-) 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; } diff --git a/net/core/dst.c b/net/core/dst.c index 80d6286c8b62..a028409ee438 100644 --- a/net/core/dst.c +++ b/net/core/dst.c @@ -269,6 +269,15 @@ again: } EXPORT_SYMBOL(dst_destroy); +static void dst_destroy_rcu(struct rcu_head *head) +{ + struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head); + + dst = dst_destroy(dst); + if (dst) + __dst_free(dst); +} + void dst_release(struct dst_entry *dst) { if (dst) { @@ -276,11 +285,8 @@ void dst_release(struct dst_entry *dst) newrefcnt = atomic_dec_return(&dst->__refcnt); WARN_ON(newrefcnt < 0); - if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) { - dst = dst_destroy(dst); - if (dst) - __dst_free(dst); - } + if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) + call_rcu(&dst->rcu_head, dst_destroy_rcu); } } EXPORT_SYMBOL(dst_release); diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 097b3e7c1e8f..54b6731dab55 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -73,12 +73,7 @@ static void __tunnel_dst_set(struct ip_tunnel_dst *idst, { struct dst_entry *old_dst; - if (dst) { - if (dst->flags & DST_NOCACHE) - dst = NULL; - else - dst_clone(dst); - } + dst_clone(dst); old_dst = xchg((__force struct dst_entry **)&idst->dst, dst); dst_release(old_dst); } @@ -108,13 +103,14 @@ static struct rtable *tunnel_rtable_get(struct ip_tunnel *t, u32 cookie) rcu_read_lock(); dst = rcu_dereference(this_cpu_ptr(t->dst_cache)->dst); + if (dst && !atomic_inc_not_zero(&dst->__refcnt)) + dst = NULL; if (dst) { if (dst->obsolete && dst->ops->check(dst, cookie) == NULL) { - rcu_read_unlock(); tunnel_dst_reset(t); - return NULL; + dst_release(dst); + dst = NULL; } - dst_hold(dst); } rcu_read_unlock(); return (struct rtable *)dst; -- 2.30.2