| From | Kamal Mostafa <> | Subject | [PATCH 3.19.y-ckt 092/102] udp: fix dst races with multicast early demux | Date | Tue, 22 Sep 2015 10:52:28 -0700 |
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3.19.8-ckt7 -stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet <edumazet@google.com>
commit 10e2eb878f3ca07ac2f05fa5ca5e6c4c9174a27a upstream.
Multicast dst are not cached. They carry DST_NOCACHE.
As mentioned in commit f8864972126899 ("ipv4: fix dst race in sk_dst_get()"), these dst need special care before caching them into a socket.
Caching them is allowed only if their refcnt was not 0, ie we must use atomic_inc_not_zero()
Also, we must use READ_ONCE() to fetch sk->sk_rx_dst, as mentioned in commit d0c294c53a771 ("tcp: prevent fetching dst twice in early demux code")
Fixes: 421b3885bf6d ("udp: ipv4: Add udp early demux") Tested-by: Gregory Hoggarth <Gregory.Hoggarth@alliedtelesis.co.nz> Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Gregory Hoggarth <Gregory.Hoggarth@alliedtelesis.co.nz> Reported-by: Alex Gartrell <agartrell@fb.com> Cc: Michal Kubeček <mkubecek@suse.cz> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- net/ipv4/udp.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index e0737ac..75f76d7 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -2001,12 +2001,19 @@ void udp_v4_early_demux(struct sk_buff *skb) skb->sk = sk; skb->destructor = sock_efree; - dst = sk->sk_rx_dst; + dst = READ_ONCE(sk->sk_rx_dst); if (dst) dst = dst_check(dst, 0); - if (dst) - skb_dst_set_noref(skb, dst); + if (dst) { + /* DST_NOCACHE can not be used without taking a reference */ + if (dst->flags & DST_NOCACHE) { + if (likely(atomic_inc_not_zero(&dst->__refcnt))) + skb_dst_set(skb, dst); + } else { + skb_dst_set_noref(skb, dst); + } + } } int udp_rcv(struct sk_buff *skb) -- 1.9.1
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