Commit 404b73e7 authored by Michal Kubeček's avatar Michal Kubeček Committed by Luis Henriques

tcp: prevent fetching dst twice in early demux code

commit d0c294c5 upstream.

On s390x, gcc 4.8 compiles this part of tcp_v6_early_demux()

        struct dst_entry *dst = sk->sk_rx_dst;

        if (dst)
                dst = dst_check(dst, inet6_sk(sk)->rx_dst_cookie);

to code reading sk->sk_rx_dst twice, once for the test and once for
the argument of ip6_dst_check() (dst_check() is inline). This allows
ip6_dst_check() to be called with null first argument, causing a crash.

Protect sk->sk_rx_dst access by READ_ONCE() both in IPv4 and IPv6
TCP early demux code.

Fixes: 41063e9d ("ipv4: Early TCP socket demux.")
Fixes: c7109986 ("ipv6: Early TCP socket demux")
Signed-off-by: default avatarMichal Kubecek <mkubecek@suse.cz>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
[ luis: backported to 3.16: used davem's backport to 3.14 ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 94cef1f5
......@@ -1637,7 +1637,7 @@ void tcp_v4_early_demux(struct sk_buff *skb)
skb->sk = sk;
skb->destructor = sock_edemux;
if (sk->sk_state != TCP_TIME_WAIT) {
struct dst_entry *dst = sk->sk_rx_dst;
struct dst_entry *dst = ACCESS_ONCE(sk->sk_rx_dst);
if (dst)
dst = dst_check(dst, 0);
......
......@@ -1646,7 +1646,7 @@ static void tcp_v6_early_demux(struct sk_buff *skb)
skb->sk = sk;
skb->destructor = sock_edemux;
if (sk->sk_state != TCP_TIME_WAIT) {
struct dst_entry *dst = sk->sk_rx_dst;
struct dst_entry *dst = ACCESS_ONCE(sk->sk_rx_dst);
if (dst)
dst = dst_check(dst, inet6_sk(sk)->rx_dst_cookie);
......
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