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authorEric Dumazet <edumazet@google.com>2014-06-24 10:05:11 -0700
committerDavid S. Miller <davem@davemloft.net>2014-06-25 17:41:44 -0700
commitf88649721268999bdff09777847080a52004f691 (patch)
tree909bff5bf235780ccec651d41bfc8a370ba7ff27 /net
parent99e72a0fed07d118d329f3046ad2ec2ae9357d63 (diff)
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 <edumazet@google.com> Reported-by: Dormando <dormando@rydia.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/dst.c16
-rw-r--r--net/ipv4/ip_tunnel.c14
2 files changed, 16 insertions, 14 deletions
diff --git a/net/core/dst.c b/net/core/dst.c
index 80d6286c8b6..a028409ee43 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 097b3e7c1e8..54b6731dab5 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;