net: add an ioctl to get a socket network namespace

Each socket operates in a network namespace where it has been created,
so if we want to dump and restore a socket, we have to know its network
namespace.

We have a socket_diag to get information about sockets, it doesn't
report sockets which are not bound or connected.

This patch introduces a new socket ioctl, which is called SIOCGSKNS
and used to get a file descriptor for a socket network namespace.

A task must have CAP_NET_ADMIN in a target network namespace to
use this ioctl.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/net/socket.c b/net/socket.c
index 5a9bf5ee2464..970a7ea3fc4a 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -877,6 +877,11 @@ static long sock_do_ioctl(struct net *net, struct socket *sock,
  *      what to do with it - that's up to the protocol still.
  */
 
+static struct ns_common *get_net_ns(struct ns_common *ns)
+{
+        return &get_net(container_of(ns, struct net, ns))->ns;
+}
+
 static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 {
         struct socket *sock;
@@ -945,6 +950,13 @@ static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
                                 err = dlci_ioctl_hook(cmd, argp);
                         mutex_unlock(&dlci_ioctl_mutex);
                         break;
+                case SIOCGSKNS:
+                        err = -EPERM;
+                        if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
+                                break;
+
+                        err = open_related_ns(&net->ns, get_net_ns);
+                        break;
                 default:
                         err = sock_do_ioctl(net, sock, cmd, arg);
                         break;
@@ -3093,6 +3105,7 @@ static int compat_sock_ioctl_trans(struct file *file, struct socket *sock,
         case SIOCSIFVLAN:
         case SIOCADDDLCI:
         case SIOCDELDLCI:
+        case SIOCGSKNS:
                 return sock_ioctl(file, cmd, arg);
 
         case SIOCGIFFLAGS: