userns: Print out socket uids in a user namespace aware fashion.

Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Sridhar Samudrala <sri@us.ibm.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
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>

net/ipv6/udp.c

@@ -1458,7 +1458,8 @@ static void udp6_sock_seq_show(struct seq_file *seq, struct sock *sp, int bucket
 		   sk_wmem_alloc_get(sp),
 		   sk_rmem_alloc_get(sp),
 		   0, 0L, 0,
-		   sock_i_uid(sp), 0,
+		   from_kuid_munged(seq_user_ns(seq), sock_i_uid(sp)),
+		   0,
 		   sock_i_ino(sp),
 		   atomic_read(&sp->sk_refcnt), sp,
 		   atomic_read(&sp->sk_drops));