net: Introduce __inet_bind() and __inet6_bind

Refactor `bind()` code to make it ready to be called from BPF helper
function `bpf_bind()` (will be added soon). Implementation of
`inet_bind()` and `inet6_bind()` is separated into `__inet_bind()` and
`__inet6_bind()` correspondingly. These function can be used from both
`sk_prot->bind` and `bpf_bind()` contexts.

New functions have two additional arguments.

`force_bind_address_no_port` forces binding to IP only w/o checking
`inet_sock.bind_address_no_port` field. It'll allow to bind local end of
a connection to desired IP in `bpf_bind()` w/o changing
`bind_address_no_port` field of a socket. It's useful since `bpf_bind()`
can return an error and we'd need to restore original value of
`bind_address_no_port` in that case if we changed this before calling to
the helper.

`with_lock` specifies whether to lock socket when working with `struct
sk` or not. The argument is set to `true` for `sk_prot->bind`, i.e. old
behavior is preserved. But it will be set to `false` for `bpf_bind()`
use-case. The reason is all call-sites, where `bpf_bind()` will be
called, already hold that socket lock.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/net/inet_common.h

@@ -32,6 +32,8 @@ int inet_shutdown(struct socket *sock, int how);
 int inet_listen(struct socket *sock, int backlog);
 void inet_sock_destruct(struct sock *sk);
 int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len);
+int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
+		bool force_bind_address_no_port, bool with_lock);
 int inet_getname(struct socket *sock, struct sockaddr *uaddr,
 		 int peer);
 int inet_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);

include/net/ipv6.h

@@ -1066,6 +1066,8 @@ void ipv6_local_error(struct sock *sk, int err, struct flowi6 *fl6, u32 info);
 void ipv6_local_rxpmtu(struct sock *sk, struct flowi6 *fl6, u32 mtu);
 
 int inet6_release(struct socket *sock);
+int __inet6_bind(struct sock *sock, struct sockaddr *uaddr, int addr_len,
+		 bool force_bind_address_no_port, bool with_lock);
 int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len);
 int inet6_getname(struct socket *sock, struct sockaddr *uaddr,
 		  int peer);

net/ipv4/af_inet.c

@@ -432,30 +432,37 @@ EXPORT_SYMBOL(inet_release);
 
 int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 {
-	struct sockaddr_in *addr = (struct sockaddr_in *)uaddr;
 	struct sock *sk = sock->sk;
-	struct inet_sock *inet = inet_sk(sk);
-	struct net *net = sock_net(sk);
-	unsigned short snum;
-	int chk_addr_ret;
-	u32 tb_id = RT_TABLE_LOCAL;
 	int err;
 
 	/* If the socket has its own bind function then use it. (RAW) */
 	if (sk->sk_prot->bind) {
-		err = sk->sk_prot->bind(sk, uaddr, addr_len);
-		goto out;
+		return sk->sk_prot->bind(sk, uaddr, addr_len);
 	}
-	err = -EINVAL;
 	if (addr_len < sizeof(struct sockaddr_in))
-		goto out;
+		return -EINVAL;
 
 	/* BPF prog is run before any checks are done so that if the prog
 	 * changes context in a wrong way it will be caught.
 	 */
 	err = BPF_CGROUP_RUN_PROG_INET4_BIND(sk, uaddr);
 	if (err)
-		goto out;
+		return err;
+
+	return __inet_bind(sk, uaddr, addr_len, false, true);
+}
+EXPORT_SYMBOL(inet_bind);
+
+int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
+		bool force_bind_address_no_port, bool with_lock)
+{
+	struct sockaddr_in *addr = (struct sockaddr_in *)uaddr;
+	struct inet_sock *inet = inet_sk(sk);
+	struct net *net = sock_net(sk);
+	unsigned short snum;
+	int chk_addr_ret;
+	u32 tb_id = RT_TABLE_LOCAL;
+	int err;
 
 	if (addr->sin_family != AF_INET) {
 		/* Compatibility games : accept AF_UNSPEC (mapped to AF_INET)
@@ -499,7 +506,8 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	 *      would be illegal to use them (multicast/broadcast) in
 	 *      which case the sending device address is used.
 	 */
-	lock_sock(sk);
+	if (with_lock)
+		lock_sock(sk);
 
 	/* Check these errors (active socket, double bind). */
 	err = -EINVAL;
@@ -511,7 +519,8 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		inet->inet_saddr = 0;  /* Use device */
 
 	/* Make sure we are allowed to bind here. */
-	if ((snum || !inet->bind_address_no_port) &&
+	if ((snum || !(inet->bind_address_no_port ||
+		       force_bind_address_no_port)) &&
 	    sk->sk_prot->get_port(sk, snum)) {
 		inet->inet_saddr = inet->inet_rcv_saddr = 0;
 		err = -EADDRINUSE;
@@ -528,11 +537,11 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	sk_dst_reset(sk);
 	err = 0;
 out_release_sock:
-	release_sock(sk);
+	if (with_lock)
+		release_sock(sk);
 out:
 	return err;
 }
-EXPORT_SYMBOL(inet_bind);
 
 int inet_dgram_connect(struct socket *sock, struct sockaddr *uaddr,
 		       int addr_len, int flags)

net/ipv6/af_inet6.c

@@ -277,15 +277,7 @@ out_rcu_unlock:
 /* bind for INET6 API */
 int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 {
-	struct sockaddr_in6 *addr = (struct sockaddr_in6 *)uaddr;
 	struct sock *sk = sock->sk;
-	struct inet_sock *inet = inet_sk(sk);
-	struct ipv6_pinfo *np = inet6_sk(sk);
-	struct net *net = sock_net(sk);
-	__be32 v4addr = 0;
-	unsigned short snum;
-	bool saved_ipv6only;
-	int addr_type = 0;
 	int err = 0;
 
 	/* If the socket has its own bind function then use it. */
@@ -302,11 +294,28 @@ int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	if (err)
 		return err;
 
+	return __inet6_bind(sk, uaddr, addr_len, false, true);
+}
+EXPORT_SYMBOL(inet6_bind);
+
+int __inet6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
+		 bool force_bind_address_no_port, bool with_lock)
+{
+	struct sockaddr_in6 *addr = (struct sockaddr_in6 *)uaddr;
+	struct inet_sock *inet = inet_sk(sk);
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct net *net = sock_net(sk);
+	__be32 v4addr = 0;
+	unsigned short snum;
+	bool saved_ipv6only;
+	int addr_type = 0;
+	int err = 0;
+
 	if (addr->sin6_family != AF_INET6)
 		return -EAFNOSUPPORT;
 
 	addr_type = ipv6_addr_type(&addr->sin6_addr);
-	if ((addr_type & IPV6_ADDR_MULTICAST) && sock->type == SOCK_STREAM)
+	if ((addr_type & IPV6_ADDR_MULTICAST) && sk->sk_type == SOCK_STREAM)
 		return -EINVAL;
 
 	snum = ntohs(addr->sin6_port);
@@ -314,7 +323,8 @@ int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	    !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE))
 		return -EACCES;
 
-	lock_sock(sk);
+	if (with_lock)
+		lock_sock(sk);
 
 	/* Check these errors (active socket, double bind). */
 	if (sk->sk_state != TCP_CLOSE || inet->inet_num) {
@@ -402,7 +412,8 @@ int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		sk->sk_ipv6only = 1;
 
 	/* Make sure we are allowed to bind here. */
-	if ((snum || !inet->bind_address_no_port) &&
+	if ((snum || !(inet->bind_address_no_port ||
+		       force_bind_address_no_port)) &&
 	    sk->sk_prot->get_port(sk, snum)) {
 		sk->sk_ipv6only = saved_ipv6only;
 		inet_reset_saddr(sk);
@@ -418,13 +429,13 @@ int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	inet->inet_dport = 0;
 	inet->inet_daddr = 0;
 out:
-	release_sock(sk);
+	if (with_lock)
+		release_sock(sk);
 	return err;
 out_unlock:
 	rcu_read_unlock();
 	goto out;
 }
-EXPORT_SYMBOL(inet6_bind);
 
 int inet6_release(struct socket *sock)
 {