SUNRPC: Fix the server AUTH_UNIX userspace mappings

gid_parse() is part of a downcall, so uids and gids should be assumed
encoded using the current user namespace.
svcauth_unix_accept() is, on the other hand, decoding uids and gids from
the wire, so we assume those are encoded to match the user namespace of
the server process.

Signed-off-by: Trond Myklebust <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

net/sunrpc/svcauth_unix.c

···
 	rv = get_int(&mesg, &id);
 	if (rv)
 		return -EINVAL;
-	uid = make_kuid(&init_user_ns, id);
+	uid = make_kuid(current_user_ns(), id);
 	ug.uid = uid;
 
 	expiry = get_expiry(&mesg);
···
 		err = -EINVAL;
 		if (rv)
 			goto out;
-		kgid = make_kgid(&init_user_ns, gid);
+		kgid = make_kgid(current_user_ns(), gid);
 		if (!gid_valid(kgid))
 			goto out;
 		ug.gi->gid[i] = kgid;
···
 			 struct cache_detail *cd,
 			 struct cache_head *h)
 {
-	struct user_namespace *user_ns = &init_user_ns;
+	struct user_namespace *user_ns = m->file->f_cred->user_ns;
 	struct unix_gid *ug;
 	int i;
 	int glen;
···
 	struct kvec	*argv = &rqstp->rq_arg.head[0];
 	struct kvec	*resv = &rqstp->rq_res.head[0];
 	struct svc_cred	*cred = &rqstp->rq_cred;
+	struct user_namespace *userns;
 	u32		slen, i;
 	int		len   = argv->iov_len;
 
···
 	 * (export-specific) anonymous id by nfsd_setuser.
 	 * Supplementary gid's will be left alone.
 	 */
-	cred->cr_uid = make_kuid(&init_user_ns, svc_getnl(argv)); /* uid */
-	cred->cr_gid = make_kgid(&init_user_ns, svc_getnl(argv)); /* gid */
+	userns = (rqstp->rq_xprt && rqstp->rq_xprt->xpt_cred) ?
+		rqstp->rq_xprt->xpt_cred->user_ns : &init_user_ns;
+	cred->cr_uid = make_kuid(userns, svc_getnl(argv)); /* uid */
+	cred->cr_gid = make_kgid(userns, svc_getnl(argv)); /* gid */
 	slen = svc_getnl(argv);			/* gids length */
 	if (slen > UNX_NGROUPS || (len -= (slen + 2)*4) < 0)
 		goto badcred;
···
 	if (cred->cr_group_info == NULL)
 		return SVC_CLOSE;
 	for (i = 0; i < slen; i++) {
-		kgid_t kgid = make_kgid(&init_user_ns, svc_getnl(argv));
+		kgid_t kgid = make_kgid(userns, svc_getnl(argv));
 		cred->cr_group_info->gid[i] = kgid;
 	}
 	groups_sort(cred->cr_group_info);