net: bpf: Handle return value of BPF_CGROUP_RUN_PROG_INET{4,6}_POST_BIND()

The return value of BPF_CGROUP_RUN_PROG_INET{4,6}_POST_BIND() in
__inet_bind() is not handled properly. While the return value
is non-zero, it will set inet_saddr and inet_rcv_saddr to 0 and
exit:

	err = BPF_CGROUP_RUN_PROG_INET4_POST_BIND(sk);
	if (err) {
		inet->inet_saddr = inet->inet_rcv_saddr = 0;
		goto out_release_sock;
	}

Let's take UDP for example and see what will happen. For UDP
socket, it will be added to 'udp_prot.h.udp_table->hash' and
'udp_prot.h.udp_table->hash2' after the sk->sk_prot->get_port()
called success. If 'inet->inet_rcv_saddr' is specified here,
then 'sk' will be in the 'hslot2' of 'hash2' that it don't belong
to (because inet_saddr is changed to 0), and UDP packet received
will not be passed to this sock. If 'inet->inet_rcv_saddr' is not
specified here, the sock will work fine, as it can receive packet
properly, which is wired, as the 'bind()' is already failed.

To undo the get_port() operation, introduce the 'put_port' field
for 'struct proto'. For TCP proto, it is inet_put_port(); For UDP
proto, it is udp_lib_unhash(); For icmp proto, it is
ping_unhash().

Therefore, after sys_bind() fail caused by
BPF_CGROUP_RUN_PROG_INET4_POST_BIND(), it will be unbinded, which
means that it can try to be binded to another port.
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220106132022.3470772-2-imagedong@tencent.com

include/net/sock.h

@@ -1209,6 +1209,7 @@ struct proto {
 	void			(*unhash)(struct sock *sk);
 	void			(*rehash)(struct sock *sk);
 	int			(*get_port)(struct sock *sk, unsigned short snum);
+	void			(*put_port)(struct sock *sk);
 #ifdef CONFIG_BPF_SYSCALL
 	int			(*psock_update_sk_prot)(struct sock *sk,
 							struct sk_psock *psock,

net/ipv4/af_inet.c

@@ -531,6 +531,8 @@ int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
 			err = BPF_CGROUP_RUN_PROG_INET4_POST_BIND(sk);
 			if (err) {
 				inet->inet_saddr = inet->inet_rcv_saddr = 0;
+				if (sk->sk_prot->put_port)
+					sk->sk_prot->put_port(sk);
 				goto out_release_sock;
 			}
 		}

net/ipv4/ping.c

@@ -994,6 +994,7 @@ struct proto ping_prot = {
 	.hash =		ping_hash,
 	.unhash =	ping_unhash,
 	.get_port =	ping_get_port,
+	.put_port =	ping_unhash,
 	.obj_size =	sizeof(struct inet_sock),
 };
 EXPORT_SYMBOL(ping_prot);

net/ipv4/tcp_ipv4.c

@@ -3076,6 +3076,7 @@ struct proto tcp_prot = {
 	.hash			= inet_hash,
 	.unhash			= inet_unhash,
 	.get_port		= inet_csk_get_port,
+	.put_port		= inet_put_port,
 #ifdef CONFIG_BPF_SYSCALL
 	.psock_update_sk_prot	= tcp_bpf_update_proto,
 #endif

net/ipv4/udp.c

@@ -2927,6 +2927,7 @@ struct proto udp_prot = {
 	.unhash			= udp_lib_unhash,
 	.rehash			= udp_v4_rehash,
 	.get_port		= udp_v4_get_port,
+	.put_port		= udp_lib_unhash,
 #ifdef CONFIG_BPF_SYSCALL
 	.psock_update_sk_prot	= udp_bpf_update_proto,
 #endif

net/ipv6/af_inet6.c

@@ -413,6 +413,8 @@ static int __inet6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
 			if (err) {
 				sk->sk_ipv6only = saved_ipv6only;
 				inet_reset_saddr(sk);
+				if (sk->sk_prot->put_port)
+					sk->sk_prot->put_port(sk);
 				goto out;
 			}
 		}

net/ipv6/ping.c

@@ -177,6 +177,7 @@ struct proto pingv6_prot = {
 	.hash =		ping_hash,
 	.unhash =	ping_unhash,
 	.get_port =	ping_get_port,
+	.put_port =	ping_unhash,
 	.obj_size =	sizeof(struct raw6_sock),
 };
 EXPORT_SYMBOL_GPL(pingv6_prot);

net/ipv6/tcp_ipv6.c

@@ -2181,6 +2181,7 @@ struct proto tcpv6_prot = {
 	.hash			= inet6_hash,
 	.unhash			= inet_unhash,
 	.get_port		= inet_csk_get_port,
+	.put_port		= inet_put_port,
 #ifdef CONFIG_BPF_SYSCALL
 	.psock_update_sk_prot	= tcp_bpf_update_proto,
 #endif

net/ipv6/udp.c

@@ -1732,6 +1732,7 @@ struct proto udpv6_prot = {
 	.unhash			= udp_lib_unhash,
 	.rehash			= udp_v6_rehash,
 	.get_port		= udp_v6_get_port,
+	.put_port		= udp_lib_unhash,
 #ifdef CONFIG_BPF_SYSCALL
 	.psock_update_sk_prot	= udp_bpf_update_proto,
 #endif