[v2,net] soreuseport: Fix TCP listener hash collision

From: Craig Gallek <kraig@google.com>

I forgot to include a check for listener port equality when deciding
if two sockets should belong to the same reuseport group.  This was
not caught previously because it's only necessary when two listening
sockets for the same user happen to hash to the same listener bucket.
This change also includes a check for network namespace equality.
The same error does not exist in the UDP path.

Fixes: c125e80b8868("soreuseport: fast reuseport TCP socket selection")
Signed-off-by: Craig Gallek <kraig@google.com>
---
v2 Changes
  - Suggestions from Eric Dumazet to include network namespace equality
    check and to avoid a dreference by simply checking inet_bind_bucket
    pointer equality.
---
 net/ipv4/inet_hashtables.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

On Thu, 2016-04-28 at 17:07 -0400, Craig Gallek wrote:
> From: Craig Gallek <kraig@google.com>
> 
> I forgot to include a check for listener port equality when deciding
> if two sockets should belong to the same reuseport group.  This was
> not caught previously because it's only necessary when two listening
> sockets for the same user happen to hash to the same listener bucket.
> This change also includes a check for network namespace equality.
> The same error does not exist in the UDP path.
> 
> Fixes: c125e80b8868("soreuseport: fast reuseport TCP socket selection")
> Signed-off-by: Craig Gallek <kraig@google.com>
> ---
> v2 Changes
>   - Suggestions from Eric Dumazet to include network namespace equality
>     check and to avoid a dreference by simply checking inet_bind_bucket
>     pointer equality.
> ---
>  net/ipv4/inet_hashtables.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index bc68eced0105..5c5658268d5e 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -470,15 +470,19 @@ static int inet_reuseport_add_sock(struct sock *sk,
>  						     const struct sock *sk2,
>  						     bool match_wildcard))
>  {
> +	struct inet_bind_bucket *tb = inet_csk(sk)->icsk_bind_hash;
> +	struct net *net = sock_net(sk);
>  	struct sock *sk2;
>  	struct hlist_nulls_node *node;
>  	kuid_t uid = sock_i_uid(sk);
>  
>  	sk_nulls_for_each_rcu(sk2, node, &ilb->head) {
> -		if (sk2 != sk &&
> +		if (net_eq(sock_net(sk2), net) &&
> +		    sk2 != sk &&
>  		    sk2->sk_family == sk->sk_family &&
>  		    ipv6_only_sock(sk2) == ipv6_only_sock(sk) &&
>  		    sk2->sk_bound_dev_if == sk->sk_bound_dev_if &&
> +		    inet_csk(sk2)->icsk_bind_hash == tb &&
>  		    sk2->sk_reuseport && uid_eq(uid, sock_i_uid(sk2)) &&
>  		    saddr_same(sk, sk2, false))
>  			return reuseport_add_sock(sk, sk2);

Note that I suggested to only use "inet_csk(sk2)->icsk_bind_hash == tb"

If test is true, it means that sockets share same name space and same
port ;)

Therefore the added net_eq(sock_net(sk2), net) test is redundant.

No strong opinion, as this patch works, and this is not fast path
anyway.

Acked-by: Eric Dumazet <edumazet@google.com>