tproxy: fix hash locking issue when using port redirection in __inet_inherit_port()

When __inet_inherit_port() is called on a tproxy connection the wrong locks are
held for the inet_bind_bucket it is added to. __inet_inherit_port() made an
implicit assumption that the listener's port number (and thus its bind bucket).
Unfortunately, if you're using the TPROXY target to redirect skbs to a
transparent proxy that assumption is not true anymore and things break.

This patch adds code to __inet_inherit_port() so that it can handle this case
by looking up or creating a new bind bucket for the child socket and updates
callers of __inet_inherit_port() to gracefully handle __inet_inherit_port()
failing.

Reported by and original patch from Stephen Buck <stephen.buck@exinda.com>.
See http://marc.info/?t=128169268200001&r=1&w=2 for the original discussion.

Signed-off-by: KOVACS Krisztian <hidden@balabit.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>

2 files changed, 33 insertions, 5 deletions

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index fb7ad5a21ff3..1b344f30b463 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -101,19 +101,43 @@ void inet_put_port(struct sock *sk)
 }
 EXPORT_SYMBOL(inet_put_port);
 
-void __inet_inherit_port(struct sock *sk, struct sock *child)
+int __inet_inherit_port(struct sock *sk, struct sock *child)
 {
         struct inet_hashinfo *table = sk->sk_prot->h.hashinfo;
-        const int bhash = inet_bhashfn(sock_net(sk), inet_sk(child)->inet_num,
+        unsigned short port = inet_sk(child)->inet_num;
+        const int bhash = inet_bhashfn(sock_net(sk), port,
                         table->bhash_size);
         struct inet_bind_hashbucket *head = &table->bhash[bhash];
         struct inet_bind_bucket *tb;
 
         spin_lock(&head->lock);
         tb = inet_csk(sk)->icsk_bind_hash;
+        if (tb->port != port) {
+                /* NOTE: using tproxy and redirecting skbs to a proxy
+                 * on a different listener port breaks the assumption
+                 * that the listener socket's icsk_bind_hash is the same
+                 * as that of the child socket. We have to look up or
+                 * create a new bind bucket for the child here. */
+                struct hlist_node *node;
+                inet_bind_bucket_for_each(tb, node, &head->chain) {
+                        if (net_eq(ib_net(tb), sock_net(sk)) &&
+                            tb->port == port)
+                                break;
+                }
+                if (!node) {
+                        tb = inet_bind_bucket_create(table->bind_bucket_cachep,
+                                                     sock_net(sk), head, port);
+                        if (!tb) {
+                                spin_unlock(&head->lock);
+                                return -ENOMEM;
+                        }
+                }
+        }
         sk_add_bind_node(child, &tb->owners);
         inet_csk(child)->icsk_bind_hash = tb;
         spin_unlock(&head->lock);
+
+        return 0;
 }
 EXPORT_SYMBOL_GPL(__inet_inherit_port);
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index a0232f3a358b..8f8527d41682 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1422,7 +1422,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 
         newsk = tcp_create_openreq_child(sk, req, skb);
         if (!newsk)
-                goto exit;
+                goto exit_nonewsk;
 
         newsk->sk_gso_type = SKB_GSO_TCPV4;
         sk_setup_caps(newsk, dst);
@@ -1469,16 +1469,20 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
         }
 #endif
 
+        if (__inet_inherit_port(sk, newsk) < 0) {
+                sock_put(newsk);
+                goto exit;
+        }
         __inet_hash_nolisten(newsk, NULL);
-        __inet_inherit_port(sk, newsk);
 
         return newsk;
 
 exit_overflow:
         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+exit_nonewsk:
+        dst_release(dst);
 exit:
         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
-        dst_release(dst);
         return NULL;
 }
 EXPORT_SYMBOL(tcp_v4_syn_recv_sock);