knfsd: nfsd: allow auth_sys nlm on rpcsec_gss exports

Our clients (like other clients, as far as I know) use only auth_sys for nlm,
even when using rpcsec_gss for the main nfs operations.

Administrators that want to deny non-kerberos-authenticated locking requests
will need to turn off NFS protocol versions less than 4....

Signed-off-by: "J. Bruce Fields" <[e-mail]>
Signed-off-by: Neil Brown <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/nfsd/nfsfh.c

···
 	if (error)
 		goto out;
 
-	/* Check security flavor */
-	error = check_nfsd_access(exp, rqstp);
-	if (error)
-		goto out;
+	if (!(access & MAY_LOCK)) {
+		/*
+		 * pseudoflavor restrictions are not enforced on NLM,
+		 * which clients virtually always use auth_sys for,
+		 * even while using RPCSEC_GSS for NFS.
+		 */
+		error = check_nfsd_access(exp, rqstp);
+		if (error)
+			goto out;
+	}
 
 	/* Finally, check access permissions. */
 	error = nfsd_permission(rqstp, exp, dentry, access);