netlink: fix compilation after memory mapped patches

Depending of the kernel configuration (CONFIG_UIDGID_STRICT_TYPE_CHECKS), we can
get the following errors:

net/netlink/af_netlink.c: In function ‘netlink_queue_mmaped_skb’:
net/netlink/af_netlink.c:663:14: error: incompatible types when assigning to type ‘__u32’ from type ‘kuid_t’
net/netlink/af_netlink.c:664:14: error: incompatible types when assigning to type ‘__u32’ from type ‘kgid_t’
net/netlink/af_netlink.c: In function ‘netlink_ring_set_copied’:
net/netlink/af_netlink.c:693:14: error: incompatible types when assigning to type ‘__u32’ from type ‘kuid_t’
net/netlink/af_netlink.c:694:14: error: incompatible types when assigning to type ‘__u32’ from type ‘kgid_t’

We must use the helpers to get the uid and gid, and also take care of user_ns.

Fix suggested by Eric W. Biederman <ebiederm@xmission.com>.
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -660,8 +660,8 @@ static void netlink_queue_mmaped_skb(struct sock *sk, struct sk_buff *skb)
 	hdr->nm_len	= skb->len;
 	hdr->nm_group	= NETLINK_CB(skb).dst_group;
 	hdr->nm_pid	= NETLINK_CB(skb).creds.pid;
-	hdr->nm_uid	= NETLINK_CB(skb).creds.uid;
-	hdr->nm_gid	= NETLINK_CB(skb).creds.gid;
+	hdr->nm_uid	= from_kuid(sk_user_ns(sk), NETLINK_CB(skb).creds.uid);
+	hdr->nm_gid	= from_kgid(sk_user_ns(sk), NETLINK_CB(skb).creds.gid);
 	netlink_frame_flush_dcache(hdr);
 	netlink_set_status(hdr, NL_MMAP_STATUS_VALID);
 
@@ -690,8 +690,8 @@ static void netlink_ring_set_copied(struct sock *sk, struct sk_buff *skb)
 	hdr->nm_len	= skb->len;
 	hdr->nm_group	= NETLINK_CB(skb).dst_group;
 	hdr->nm_pid	= NETLINK_CB(skb).creds.pid;
-	hdr->nm_uid	= NETLINK_CB(skb).creds.uid;
-	hdr->nm_gid	= NETLINK_CB(skb).creds.gid;
+	hdr->nm_uid	= from_kuid(sk_user_ns(sk), NETLINK_CB(skb).creds.uid);
+	hdr->nm_gid	= from_kgid(sk_user_ns(sk), NETLINK_CB(skb).creds.gid);
 	netlink_set_status(hdr, NL_MMAP_STATUS_COPY);
 }