On Mon, 2015-03-23 at 09:27 +0100, Michal Kubecek wrote:
> 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 ACCESS_ONCE() both in IPv4 and IPv6
> TCP early demux code.
>
> Fixes: 41063e9dd119 ("ipv4: Early TCP socket demux.")
> Fixes: c7109986db3c ("ipv6: Early TCP socket demux")
>
Please remove this empty line. "Fixes" tags should be in the final group
of tags.
> Signed-off-by: Michal Kubecek <[email protected]>
> ---
> net/ipv4/tcp_ipv4.c | 2 +-
> net/ipv6/tcp_ipv6.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 5a2dfed..3d42b45 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1518,7 +1518,7 @@ 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 5d46832..50eb5ff 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1585,7 +1585,7 @@ 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);
Good catch, (or would I say, strange compiler ? ;) )
Please use READ_ONCE(). Only stable ports will need ACCESS_ONCE()
Also, this probably points a problem on this arch, because its looks
different cpu are handling TCP traffic for the same TCP flow.
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