Subject: [PATCH v2 4/4] net: diag: Support destroying TCP sockets.

From: Lorenzo Colitti <[email-masked]>
Date: Wed, 18 Nov 2015 13:41:03 +0900

This implements SOCK_DESTROY for TCP sockets. It causes all
blocking calls on the socket to fail fast with ETIMEDOUT, which
is the same thing that would eventually happen if the socket was
left stuck on an IP address that the host no longer has.

Signed-off-by: Lorenzo Colitti <[email-masked]>
---
 net/ipv4/tcp_diag.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/net/ipv4/tcp_diag.c b/net/ipv4/tcp_diag.c
index b316040..867159c 100644
--- a/net/ipv4/tcp_diag.c
+++ b/net/ipv4/tcp_diag.c
@@ -10,6 +10,7 @@
  */
 
 #include <linux/module.h>
+#include <linux/net.h>
 #include <linux/inet_diag.h>
 
 #include <linux/tcp.h>
@@ -46,12 +47,52 @@ 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);
 }
 
+static int tcp_diag_destroy(struct sk_buff *in_skb,
+			    const struct inet_diag_req_v2 *req)
+{
+	struct sock *sk;
+	struct net *net = sock_net(in_skb->sk);
+
+	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
+		return -EPERM;
+
+	sk = inet_diag_find_one_icsk(net, &tcp_hashinfo, req);
+	if (IS_ERR(sk))
+		return PTR_ERR(sk);
+
+	if (!sk_fullsock(sk)) {
+		sock_gen_put(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)) {
+		smp_wmb();  /* Be consistent with tcp_reset */
+		sk->sk_err = ETIMEDOUT;
+		sk->sk_error_report(sk);
+		tcp_done(sk);
+	}
+
+	bh_unlock_sock(sk);
+	local_bh_enable();
+	release_sock(sk);
+	sock_put(sk);
+	return 0;
+}
+
 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,
 	.idiag_info_size = sizeof(struct tcp_info),
+	.destroy	 = tcp_diag_destroy,
 };
 
 static int __init tcp_diag_init(void)
-- 
2.6.0.rc2.230.g3dd15c0