[REPOST PATCH xauth] Look for FamilyLocal if inet or inet6 address is loopback

[Egbert Eich]

libxcb uses FamilyLocal authorization if the host name or IP in the
display string is from the loopback device. This patch adds the same
behavior to xauth.
This fixes a long standing problem that for ssh tunneled connections
a display variable of the form: localhost:<N>.<M> leads to correct
authorization when an X client is started but "xauth list $DISPLAY"
returns nothing.

Signed-off-by: Egbert Eich <eich at freedesktop.org>
---
 gethost.c | 40 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/gethost.c b/gethost.c
index 10f6078..83fa95b 100644
--- a/gethost.c
+++ b/gethost.c
@@ -224,16 +224,36 @@ struct addrlist *get_address_info (
 	for (ai = firstai; ai != NULL; ai = ai->ai_next) {
 	    struct addrlist *duplicate;
 
+            len = 0;
 	    if (ai->ai_family == AF_INET) {
 		struct sockaddr_in *sin = (struct sockaddr_in *)ai->ai_addr;
 		src = &(sin->sin_addr);
-		len = sizeof(sin->sin_addr);
-		family = FamilyInternet;
+                if (*(in_addr_t *) src == htonl(INADDR_LOOPBACK)) {
+                    family = FamilyLocal;
+                    if (get_local_hostname (buf, sizeof buf)) {
+                        src = buf;
+                        len = strlen (buf);
+                    } else
+                        src = NULL;
+                } else {
+                    len = sizeof(sin->sin_addr);
+                    family = FamilyInternet;
+                }
 	    } else if (ai->ai_family == AF_INET6) {
 		struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)ai->ai_addr;
 		src = &(sin6->sin6_addr);
-		len = sizeof(sin6->sin6_addr);
-		family = FamilyInternet6;
+                if (IN6_IS_ADDR_V4MAPPED((struct sockaddr_in6 *)src)
+                    || IN6_IS_ADDR_LOOPBACK((struct sockaddr_in6 *)src)) {
+                    family = FamilyLocal;
+                    if (get_local_hostname (buf, sizeof buf)) {
+                        src = buf;
+                        len = strlen (buf);
+                    } else
+                        src = NULL;
+                } else {
+                    len = sizeof(sin6->sin6_addr);
+                    family = FamilyInternet6;
+                }
 	    }
 
 	    for(duplicate = retval; duplicate != NULL; duplicate = duplicate->next) {
@@ -272,7 +292,17 @@ struct addrlist *get_address_info (
 #else
 	if (!get_inet_address (host, &hostinetaddr)) return NULL;
 	src = (char *) &hostinetaddr;
-	len = 4; /* sizeof inaddr.sin_addr, would fail on Cray */
+        if (*(in_addr_t *) src == htonl(INADDR_LOOPBACK)) {
+            family = FamilyLocal;
+            if (get_local_hostname (buf, sizeof buf)) {
+                src = buf;
+                len = strlen (buf);
+            } else {
+                len = 0;
+                src = NULL;
+            }
+        } else
+            len = 4; /* sizeof inaddr.sin_addr, would fail on Cray */
 	break;
 #endif /* IPv6 */
 #else
-- 
1.8.1.4