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Date: Fri, 8 Aug 2014 13:41:00 -0700 From: Kamal Mostafa <kamal@...onical.com> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...ts.ubuntu.com Cc: Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, Luis Henriques <luis.henriques@...onical.com>, Kamal Mostafa <kamal@...onical.com> Subject: [PATCH 3.13 237/259] ipv4: fix dst race in sk_dst_get() 3.13.11.6 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet <edumazet@...gle.com> commit f88649721268999bdff09777847080a52004f691 upstream. 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@...gle.com> Reported-by: Dormando <dormando@...ia.net> Signed-off-by: David S. Miller <davem@...emloft.net> [ luis: backported to 3.11: used davem's backport to 3.10 ] Signed-off-by: Luis Henriques <luis.henriques@...onical.com> Signed-off-by: Kamal Mostafa <kamal@...onical.com> --- include/net/sock.h | 4 ++-- net/core/dst.c | 16 +++++++++++----- 2 files changed, 13 insertions(+), 7 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index ca1aeeb..e7ad8ac 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1743,8 +1743,8 @@ 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 ca4231e..15b6792 100644 --- a/net/core/dst.c +++ b/net/core/dst.c @@ -267,6 +267,15 @@ 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) { @@ -274,11 +283,8 @@ 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); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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