l2tp: prevent tunnel creation on netns mismatch

l2tp_tunnel_create is passed a pointer to the network namespace for the
tunnel, along with an optional file descriptor for the tunnel which may
be passed in from userspace via. netlink.

In the case where the file descriptor is defined, ensure that the namespace
associated with that socket matches the namespace explicitly passed to
l2tp_tunnel_create.

Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 2 deletions

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 73988c070561..60a498a459dd 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1593,11 +1593,18 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
                 if (err < 0)
                         goto err;
         } else {
-                err = -EBADF;
                 sock = sockfd_lookup(fd, &err);
                 if (!sock) {
-                        pr_err("tunl %hu: sockfd_lookup(fd=%d) returned %d\n",
+                        pr_err("tunl %u: sockfd_lookup(fd=%d) returned %d\n",
                                tunnel_id, fd, err);
+                        err = -EBADF;
+                        goto err;
+                }
+
+                /* Reject namespace mismatches */
+                if (!net_eq(sock_net(sock->sk), net)) {
+                        pr_err("tunl %u: netns mismatch\n", tunnel_id);
+                        err = -EINVAL;
                         goto err;
                 }
         }