Merge branch 'net-initialize-fastreuse-on-inet_inherit_port'

Tim Froidcoeur says:

====================
net: initialize fastreuse on inet_inherit_port

In the case of TPROXY, bind_conflict optimizations for SO_REUSEADDR or
SO_REUSEPORT are broken, possibly resulting in O(n) instead of O(1) bind
behaviour or in the incorrect reuse of a bind.

the kernel keeps track for each bind_bucket if all sockets in the
bind_bucket support SO_REUSEADDR or SO_REUSEPORT in two fastreuse flags.
These flags allow skipping the costly bind_conflict check when possible
(meaning when all sockets have the proper SO_REUSE option).

For every socket added to a bind_bucket, these flags need to be updated.
As soon as a socket that does not support reuse is added, the flag is
set to false and will never go back to true, unless the bind_bucket is
deleted.

Note that there is no mechanism to re-evaluate these flags when a socket
is removed (this might make sense when removing a socket that would not
allow reuse; this leaves room for a future patch).

For this optimization to work, it is mandatory that these flags are
properly initialized and updated.

When a child socket is created from a listen socket in
__inet_inherit_port, the TPROXY case could create a new bind bucket
without properly initializing these flags, thus preventing the
optimization to work. Alternatively, a socket not allowing reuse could
be added to an existing bind bucket without updating the flags, causing
bind_conflict to never be called as it should.

Patch 1/2 refactors the fastreuse update code in inet_csk_get_port into a
small helper function, making the actual fix tiny and easier to understand.

Patch 2/2 calls this new helper when __inet_inherit_port decides to create
a new bind_bucket or use a different bind_bucket than the one of the listen
socket.

v4: - rebase on latest linux/net master branch
v3: - remove company disclaimer from automatic signature
v2: - remove unnecessary cast
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_connection_sock.h

@@ -304,6 +304,10 @@ void inet_csk_listen_stop(struct sock *sk);
 
 void inet_csk_addr2sockaddr(struct sock *sk, struct sockaddr *uaddr);
 
+/* update the fast reuse flag when adding a socket */
+void inet_csk_update_fastreuse(struct inet_bind_bucket *tb,
+			       struct sock *sk);
+
 struct dst_entry *inet_csk_update_pmtu(struct sock *sk, u32 mtu);
 
 #define TCP_PINGPONG_THRESH	3

net/ipv4/inet_connection_sock.c

@@ -296,55 +296,12 @@ static inline int sk_reuseport_match(struct inet_bind_bucket *tb,
 				    ipv6_only_sock(sk), true, false);
 }
 
-/* Obtain a reference to a local port for the given sock,
- * if snum is zero it means select any available local port.
- * We try to allocate an odd port (and leave even ports for connect())
- */
-int inet_csk_get_port(struct sock *sk, unsigned short snum)
+void inet_csk_update_fastreuse(struct inet_bind_bucket *tb,
+			       struct sock *sk)
 {
-	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
-	struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
-	int ret = 1, port = snum;
-	struct inet_bind_hashbucket *head;
-	struct net *net = sock_net(sk);
-	struct inet_bind_bucket *tb = NULL;
 	kuid_t uid = sock_i_uid(sk);
-	int l3mdev;
+	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
 
-	l3mdev = inet_sk_bound_l3mdev(sk);
-
-	if (!port) {
-		head = inet_csk_find_open_port(sk, &tb, &port);
-		if (!head)
-			return ret;
-		if (!tb)
-			goto tb_not_found;
-		goto success;
-	}
-	head = &hinfo->bhash[inet_bhashfn(net, port,
-					  hinfo->bhash_size)];
-	spin_lock_bh(&head->lock);
-	inet_bind_bucket_for_each(tb, &head->chain)
-		if (net_eq(ib_net(tb), net) && tb->l3mdev == l3mdev &&
-		    tb->port == port)
-			goto tb_found;
-tb_not_found:
-	tb = inet_bind_bucket_create(hinfo->bind_bucket_cachep,
-				     net, head, port, l3mdev);
-	if (!tb)
-		goto fail_unlock;
-tb_found:
-	if (!hlist_empty(&tb->owners)) {
-		if (sk->sk_reuse == SK_FORCE_REUSE)
-			goto success;
-
-		if ((tb->fastreuse > 0 && reuse) ||
-		    sk_reuseport_match(tb, sk))
-			goto success;
-		if (inet_csk_bind_conflict(sk, tb, true, true))
-			goto fail_unlock;
-	}
-success:
 	if (hlist_empty(&tb->owners)) {
 		tb->fastreuse = reuse;
 		if (sk->sk_reuseport) {
@@ -388,6 +345,58 @@ success:
 			tb->fastreuseport = 0;
 		}
 	}
+}
+
+/* Obtain a reference to a local port for the given sock,
+ * if snum is zero it means select any available local port.
+ * We try to allocate an odd port (and leave even ports for connect())
+ */
+int inet_csk_get_port(struct sock *sk, unsigned short snum)
+{
+	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
+	struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
+	int ret = 1, port = snum;
+	struct inet_bind_hashbucket *head;
+	struct net *net = sock_net(sk);
+	struct inet_bind_bucket *tb = NULL;
+	int l3mdev;
+
+	l3mdev = inet_sk_bound_l3mdev(sk);
+
+	if (!port) {
+		head = inet_csk_find_open_port(sk, &tb, &port);
+		if (!head)
+			return ret;
+		if (!tb)
+			goto tb_not_found;
+		goto success;
+	}
+	head = &hinfo->bhash[inet_bhashfn(net, port,
+					  hinfo->bhash_size)];
+	spin_lock_bh(&head->lock);
+	inet_bind_bucket_for_each(tb, &head->chain)
+		if (net_eq(ib_net(tb), net) && tb->l3mdev == l3mdev &&
+		    tb->port == port)
+			goto tb_found;
+tb_not_found:
+	tb = inet_bind_bucket_create(hinfo->bind_bucket_cachep,
+				     net, head, port, l3mdev);
+	if (!tb)
+		goto fail_unlock;
+tb_found:
+	if (!hlist_empty(&tb->owners)) {
+		if (sk->sk_reuse == SK_FORCE_REUSE)
+			goto success;
+
+		if ((tb->fastreuse > 0 && reuse) ||
+		    sk_reuseport_match(tb, sk))
+			goto success;
+		if (inet_csk_bind_conflict(sk, tb, true, true))
+			goto fail_unlock;
+	}
+success:
+	inet_csk_update_fastreuse(tb, sk);
+
 	if (!inet_csk(sk)->icsk_bind_hash)
 		inet_bind_hash(sk, tb, port);
 	WARN_ON(inet_csk(sk)->icsk_bind_hash != tb);

net/ipv4/inet_hashtables.c

@@ -163,6 +163,7 @@ int __inet_inherit_port(const struct sock *sk, struct sock *child)
 				return -ENOMEM;
 			}
 		}
+		inet_csk_update_fastreuse(tb, child);
 	}
 	inet_bind_hash(child, tb, port);
 	spin_unlock(&head->lock);