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

@@ -296,6 +296,57 @@ static inline int sk_reuseport_match(struct inet_bind_bucket *tb,
 				    ipv6_only_sock(sk), true, false);
 }
 
+void inet_csk_update_fastreuse(struct inet_bind_bucket *tb,
+			       struct sock *sk)
+{
+	kuid_t uid = sock_i_uid(sk);
+	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
+
+	if (hlist_empty(&tb->owners)) {
+		tb->fastreuse = reuse;
+		if (sk->sk_reuseport) {
+			tb->fastreuseport = FASTREUSEPORT_ANY;
+			tb->fastuid = uid;
+			tb->fast_rcv_saddr = sk->sk_rcv_saddr;
+			tb->fast_ipv6_only = ipv6_only_sock(sk);
+			tb->fast_sk_family = sk->sk_family;
+#if IS_ENABLED(CONFIG_IPV6)
+			tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
+#endif
+		} else {
+			tb->fastreuseport = 0;
+		}
+	} else {
+		if (!reuse)
+			tb->fastreuse = 0;
+		if (sk->sk_reuseport) {
+			/* We didn't match or we don't have fastreuseport set on
+			 * the tb, but we have sk_reuseport set on this socket
+			 * and we know that there are no bind conflicts with
+			 * this socket in this tb, so reset our tb's reuseport
+			 * settings so that any subsequent sockets that match
+			 * our current socket will be put on the fast path.
+			 *
+			 * If we reset we need to set FASTREUSEPORT_STRICT so we
+			 * do extra checking for all subsequent sk_reuseport
+			 * socks.
+			 */
+			if (!sk_reuseport_match(tb, sk)) {
+				tb->fastreuseport = FASTREUSEPORT_STRICT;
+				tb->fastuid = uid;
+				tb->fast_rcv_saddr = sk->sk_rcv_saddr;
+				tb->fast_ipv6_only = ipv6_only_sock(sk);
+				tb->fast_sk_family = sk->sk_family;
+#if IS_ENABLED(CONFIG_IPV6)
+				tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
+#endif
+			}
+		} else {
+			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())
@@ -308,7 +359,6 @@ int inet_csk_get_port(struct sock *sk, unsigned short 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;
 
 	l3mdev = inet_sk_bound_l3mdev(sk);
@@ -345,49 +395,8 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
 			goto fail_unlock;
 	}
 success:
-	if (hlist_empty(&tb->owners)) {
-		tb->fastreuse = reuse;
-		if (sk->sk_reuseport) {
-			tb->fastreuseport = FASTREUSEPORT_ANY;
-			tb->fastuid = uid;
-			tb->fast_rcv_saddr = sk->sk_rcv_saddr;
-			tb->fast_ipv6_only = ipv6_only_sock(sk);
-			tb->fast_sk_family = sk->sk_family;
-#if IS_ENABLED(CONFIG_IPV6)
-			tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
-#endif
-		} else {
-			tb->fastreuseport = 0;
-		}
-	} else {
-		if (!reuse)
-			tb->fastreuse = 0;
-		if (sk->sk_reuseport) {
-			/* We didn't match or we don't have fastreuseport set on
-			 * the tb, but we have sk_reuseport set on this socket
-			 * and we know that there are no bind conflicts with
-			 * this socket in this tb, so reset our tb's reuseport
-			 * settings so that any subsequent sockets that match
-			 * our current socket will be put on the fast path.
-			 *
-			 * If we reset we need to set FASTREUSEPORT_STRICT so we
-			 * do extra checking for all subsequent sk_reuseport
-			 * socks.
-			 */
-			if (!sk_reuseport_match(tb, sk)) {
-				tb->fastreuseport = FASTREUSEPORT_STRICT;
-				tb->fastuid = uid;
-				tb->fast_rcv_saddr = sk->sk_rcv_saddr;
-				tb->fast_ipv6_only = ipv6_only_sock(sk);
-				tb->fast_sk_family = sk->sk_family;
-#if IS_ENABLED(CONFIG_IPV6)
-				tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
-#endif
-			}
-		} else {
-			tb->fastreuseport = 0;
-		}
-	}
+	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);