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udp: fix dst races with multicast early demux

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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>
This commit is contained in:
Eric Dumazet 2015-08-01 12:14:33 +02:00 committed by David S. Miller
parent 2fc09962e2
commit 10e2eb878f
1 changed files with 10 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
net/ipv4/udp.c
View File

@ -1995,12 +1995,19 @@ 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)