net: diag: Support destroying TCP sockets.

This implements SOCK_DESTROY for TCP sockets. It causes all
blocking calls on the socket to fail fast with ECONNABORTED and
causes a protocol close of the socket. It informs the other end
of the connection by sending a RST, i.e., initiating a TCP ABORT
as per RFC 793. ECONNABORTED was chosen for consistency with
FreeBSD.

[Backport of net-next c1e64e298b8cad309091b95d8436a0255c84f54a]

Change-Id: Ic5410d3a2f39db28a322c30f4b3b2bffd35ec2de
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -997,6 +997,8 @@ extern void tcp_set_state(struct sock *sk, int state);
 
 extern void tcp_done(struct sock *sk);
 
+int tcp_abort(struct sock *sk, int err);
+
 static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
 {
 	rx_opt->dsack = 0;

net/ipv4/Kconfig

@@ -415,6 +415,19 @@ config INET_UDP_DIAG
 	  Support for UDP socket monitoring interface used by the ss tool.
 	  If unsure, say Y.
 
+config INET_DIAG_DESTROY
+	bool "INET: allow privileged process to administratively close sockets"
+	depends on INET_DIAG
+	default n
+	---help---
+	  Provides a SOCK_DESTROY_BACKPORT operation that allows privileged processes
+	  (e.g., a connection manager or a network administration tool such as
+	  ss) to close sockets opened by other processes. Closing a socket in
+	  this way interrupts any blocking read/write/connect operations on
+	  the socket and causes future socket calls to behave as if the socket
+	  had been disconnected.
+	  If unsure, say N.
+
 menuconfig TCP_CONG_ADVANCED
 	bool "TCP: advanced congestion control"
 	---help---

net/ipv4/tcp.c

@@ -3251,6 +3251,38 @@ void tcp_done(struct sock *sk)
 }
 EXPORT_SYMBOL_GPL(tcp_done);
 
+int tcp_abort(struct sock *sk, int err)
+{
+	if (sk->sk_state == TCP_TIME_WAIT) {
+		inet_twsk_put((struct inet_timewait_sock *)sk);
+		return -EOPNOTSUPP;
+	}
+
+	/* Don't race with userspace socket closes such as tcp_close. */
+	lock_sock(sk);
+
+	/* Don't race with BH socket closes such as inet_csk_listen_stop. */
+	local_bh_disable();
+	bh_lock_sock(sk);
+
+	if (!sock_flag(sk, SOCK_DEAD)) {
+		sk->sk_err = err;
+		/* This barrier is coupled with smp_rmb() in tcp_poll() */
+		smp_wmb();
+		sk->sk_error_report(sk);
+		if (tcp_need_reset(sk->sk_state))
+			tcp_send_active_reset(sk, GFP_ATOMIC);
+		tcp_done(sk);
+	}
+
+	bh_unlock_sock(sk);
+	local_bh_enable();
+	release_sock(sk);
+	sock_put(sk);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tcp_abort);
+
 extern struct tcp_congestion_ops tcp_reno;
 
 static __initdata unsigned long thash_entries;

net/ipv4/tcp_diag.c

@@ -11,6 +11,8 @@
 
 
 #include <linux/module.h>
+#include <linux/net.h>
+#include <linux/sock_diag.h>
 #include <linux/inet_diag.h>
 
 #include <linux/tcp.h>
@@ -46,11 +48,28 @@ static int tcp_diag_dump_one(struct sk_buff *in_skb, const struct nlmsghdr *nlh,
 	return inet_diag_dump_one_icsk(&tcp_hashinfo, in_skb, nlh, req);
 }
 
+#ifdef CONFIG_INET_DIAG_DESTROY
+static int tcp_diag_destroy(struct sk_buff *in_skb,
+			    struct inet_diag_req_v2 *req)
+{
+	struct net *net = sock_net(in_skb->sk);
+	struct sock *sk = inet_diag_find_one_icsk(net, &tcp_hashinfo, req);
+
+	if (IS_ERR(sk))
+		return PTR_ERR(sk);
+
+	return sock_diag_destroy(sk, ECONNABORTED);
+}
+#endif
+
 static const struct inet_diag_handler tcp_diag_handler = {
 	.dump		 = tcp_diag_dump,
 	.dump_one	 = tcp_diag_dump_one,
 	.idiag_get_info	 = tcp_diag_get_info,
 	.idiag_type	 = IPPROTO_TCP,
+#ifdef CONFIG_INET_DIAG_DESTROY
+	.destroy	 = tcp_diag_destroy,
+#endif
 };
 
 static int __init tcp_diag_init(void)

net/ipv4/tcp_ipv4.c

@@ -2663,6 +2663,7 @@ struct proto tcp_prot = {
 	.destroy_cgroup		= tcp_destroy_cgroup,
 	.proto_cgroup		= tcp_proto_cgroup,
 #endif
+	.diag_destroy		= tcp_abort,
 };
 EXPORT_SYMBOL(tcp_prot);
 

net/ipv6/tcp_ipv6.c

@@ -2146,6 +2146,7 @@ struct proto tcpv6_prot = {
 	.proto_cgroup		= tcp_proto_cgroup,
 #endif
 	.clear_sk		= tcp_v6_clear_sk,
+	.diag_destroy		= tcp_abort,
 };
 
 static const struct inet6_protocol tcpv6_protocol = {