[PATCH v5 1/4] net: diag: Add the ability to destroy a socket.

[Lorenzo Colitti <lorenzo@google.com>]

This adds a diag_destroy pointer to struct proto that allows a
socket to be administratively closed without any action from the
process owning the socket or the socket protocol.

This allows a privileged userspace process, such as a connection
manager or system administration tool, to close sockets belonging
to other apps when the network they were established on has
disconnected. It is needed on laptops and mobile hosts to ensure
that network switches / disconnects do not result in applications
being blocked for long periods of time (minutes) in read or
connect calls on TCP sockets that will never succeed because the
IP address they are bound to is no longer on the system. Closing
the sockets causes these calls to fail fast and allows the apps
to reconnect on another network.

For many years Android kernels have supported this via an
out-of-tree SIOCKILLADDR ioctl that is called on every
RTM_DELADDR event, but this solution is cleaner, more robust and
more flexible: the connection manager can iterate over all
connections on the deleted IP address and close all of them. It
can also be used to close all sockets opened by a given app
process, for example if the user has restricted that app from
using the network.

It also allows in-kernel callers to perform the same sort of
operation by invoking sk->sk_prot->diag_destroy(sk) directly.

This patch adds a SOCK_DESTROY operation, a destroy function
pointer to sock_diag_handler, and a diag_destroy function
pointer.  It does not include any implementation code.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
---
 include/linux/sock_diag.h      |  2 ++
 include/net/sock.h             |  1 +
 include/uapi/linux/sock_diag.h |  1 +
 net/core/sock_diag.c           | 23 ++++++++++++++++++++---
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/include/linux/sock_diag.h b/include/linux/sock_diag.h
index fddebc6..15072fc 100644
--- a/include/linux/sock_diag.h
+++ b/include/linux/sock_diag.h
@@ -15,6 +15,7 @@ struct sock_diag_handler {
 	__u8 family;
 	int (*dump)(struct sk_buff *skb, struct nlmsghdr *nlh);
 	int (*get_info)(struct sk_buff *skb, struct sock *sk);
+	int (*destroy)(struct sk_buff *skb, struct nlmsghdr *nlh);
 };
 
 int sock_diag_register(const struct sock_diag_handler *h);
@@ -68,4 +69,5 @@ bool sock_diag_has_destroy_listeners(const struct sock *sk)
 }
 void sock_diag_broadcast_destroy(struct sock *sk);
 
+int sock_diag_destroy(struct sock *sk);
 #endif
diff --git a/include/net/sock.h b/include/net/sock.h
index 0ca22b0..a1b30d7f 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1060,6 +1060,7 @@ struct proto {
 	void			(*destroy_cgroup)(struct mem_cgroup *memcg);
 	struct cg_proto		*(*proto_cgroup)(struct mem_cgroup *memcg);
 #endif
+	int			(*diag_destroy)(struct sock *sk);
 };
 
 int proto_register(struct proto *prot, int alloc_slab);
diff --git a/include/uapi/linux/sock_diag.h b/include/uapi/linux/sock_diag.h
index 49230d3..bae2d80 100644
--- a/include/uapi/linux/sock_diag.h
+++ b/include/uapi/linux/sock_diag.h
@@ -4,6 +4,7 @@
 #include <linux/types.h>
 
 #define SOCK_DIAG_BY_FAMILY 20
+#define SOCK_DESTROY 21
 
 struct sock_diag_req {
 	__u8	sdiag_family;
diff --git a/net/core/sock_diag.c b/net/core/sock_diag.c
index 0c1d58d..967d89f 100644
--- a/net/core/sock_diag.c
+++ b/net/core/sock_diag.c
@@ -214,7 +214,7 @@ void sock_diag_unregister(const struct sock_diag_handler *hnld)
 }
 EXPORT_SYMBOL_GPL(sock_diag_unregister);
 
-static int __sock_diag_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
+static int __sock_diag_cmd(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
 	int err;
 	struct sock_diag_req *req = nlmsg_data(nlh);
@@ -234,8 +234,12 @@ static int __sock_diag_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 	hndl = sock_diag_handlers[req->sdiag_family];
 	if (hndl == NULL)
 		err = -ENOENT;
-	else
+	else if (nlh->nlmsg_type == SOCK_DIAG_BY_FAMILY)
 		err = hndl->dump(skb, nlh);
+	else if (nlh->nlmsg_type == SOCK_DESTROY && hndl->destroy)
+		err = hndl->destroy(skb, nlh);
+	else
+		err = -EOPNOTSUPP;
 	mutex_unlock(&sock_diag_table_mutex);
 
 	return err;
@@ -261,7 +265,8 @@ static int sock_diag_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 
 		return ret;
 	case SOCK_DIAG_BY_FAMILY:
-		return __sock_diag_rcv_msg(skb, nlh);
+	case SOCK_DESTROY:
+		return __sock_diag_cmd(skb, nlh);
 	default:
 		return -EINVAL;
 	}
@@ -295,6 +300,18 @@ static int sock_diag_bind(struct net *net, int group)
 	return 0;
 }
 
+int sock_diag_destroy(struct sock *sk)
+{
+	if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (!sk->sk_prot->diag_destroy)
+		return -EOPNOTSUPP;
+
+	return sk->sk_prot->diag_destroy(sk);
+}
+EXPORT_SYMBOL_GPL(sock_diag_destroy);
+
 static int __net_init diag_net_init(struct net *net)
 {
 	struct netlink_kernel_cfg cfg = {
-- 
2.6.0.rc2.230.g3dd15c0