userns: Implement sk_user_ns

Add a helper sk_user_ns to make it easy to find the user namespace
of the process that opened a socket.

Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 65c3d62bfa5a..9d43736a869d 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -604,6 +604,15 @@ static inline void sk_add_bind_node(struct sock *sk,
 #define sk_for_each_bound(__sk, node, list) \
         hlist_for_each_entry(__sk, node, list, sk_bind_node)
 
+static inline struct user_namespace *sk_user_ns(struct sock *sk)
+{
+        /* Careful only use this in a context where these parameters
+         * can not change and must all be valid, such as recvmsg from
+         * userspace.
+         */
+        return sk->sk_socket->file->f_cred->user_ns;
+}
+
 /* Sock flags */
 enum sock_flags {
         SOCK_DEAD,