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| author | Eric Dumazet <edumazet@google.com> | 2015-08-01 12:14:33 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-10-01 11:36:24 +0200 |
| commit | e602c012fd2d30cba979bc5b51bc3e5b52cc9065 (patch) | |
| tree | 14da378228881c22101fc85da81148cf757a3936 | |
| parent | ef9fff760b034f17c113944efb6b0b3b29321a45 (diff) | |
| download | lwn-e602c012fd2d30cba979bc5b51bc3e5b52cc9065.tar.gz lwn-e602c012fd2d30cba979bc5b51bc3e5b52cc9065.zip | |
udp: fix dst races with multicast early demux
[ Upstream commit 10e2eb878f3ca07ac2f05fa5ca5e6c4c9174a27a ]
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | net/ipv4/udp.c | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 21a3a9e90b10..947dcae8a77a 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1957,12 +1957,19 @@ void udp_v4_early_demux(struct sk_buff *skb) skb->sk = sk; skb->destructor = sock_edemux; - dst = sk->sk_rx_dst; + dst = ACCESS_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) |