NLM: nlm_privileged_requester() doesn't recognize mapped loopback address

Commit b85e4676 added the nlm_privileged_requester() helper to check
whether an RPC request was sent from a local privileged caller.  It
recognizes IPv4 privileged callers (from "127.0.0.1"), and IPv6
privileged callers (from "::1").

However, IPV6_ADDR_LOOPBACK is not set for the mapped IPv4 loopback
address (::ffff:7f00:0001), so the test breaks when the kernel's RPC
service is IPv6-enabled but user space is calling via the IPv4
loopback address.  This is actually the most common case for IPv6-
enabled RPC services on Linux.

Rewrite the IPv6 check to handle the mapped IPv4 loopback address as
well as a normal IPv6 loopback address.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 8 insertions, 2 deletions

diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index 6ab0449bc828..80d7e8a8257d 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -299,8 +299,14 @@ static inline int __nlm_privileged_request4(const struct sockaddr *sap)
 static inline int __nlm_privileged_request6(const struct sockaddr *sap)
 {
         const struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)sap;
-        return (ipv6_addr_type(&sin6->sin6_addr) & IPV6_ADDR_LOOPBACK) &&
-                        (ntohs(sin6->sin6_port) < 1024);
+
+        if (ntohs(sin6->sin6_port) > 1023)
+                return 0;
+
+        if (ipv6_addr_type(&sin6->sin6_addr) & IPV6_ADDR_MAPPED)
+                return ipv4_is_loopback(sin6->sin6_addr.s6_addr32[3]);
+
+        return ipv6_addr_type(&sin6->sin6_addr) & IPV6_ADDR_LOOPBACK;
 }
 #else   /* defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) */
 static inline int __nlm_privileged_request6(const struct sockaddr *sap)