tcp: prevent fetching dst twice in early demux code

commit d0c294c53a771ae7e84506dfbd8c18c30f078735 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: 41063e9dd119 ("ipv4: Early TCP socket demux.")
Fixes: c7109986db3c ("ipv6: Early TCP socket demux")
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ luis: backported to 3.16: used davem's backport to 3.14 ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index ac7752f4f7771d710b696fd021cc6e96ed36f2b8..b68fd0d65411abaadd5d22d17e082b5c161419c1 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -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);

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index cb5125c5328d5bf0aa88abe5333857bf29ba3601..d15a5484076f33b7a58c127f494ef756942f2e3b 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -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);