login: use IPv4 on IPv4-mapping-to-IPv6

It seems that on some systems (e.g. RHEL7) the libc function
getaddrinfo() is not able to translate ::ffff: address to IPv4. The
result is 0.0.0.0 host address in the last(1) and utmpdump(1) output.

 /sbin/login -h "::ffff:192.168.1.7"

utmpdump:

  [7] [03926] [1   ] [user1   ] [pts/1       ] [::ffff:192.168.1.7  ] [0.0.0.0        ] [Thu May 12 17:49:50 2016    ]

Not sure if this is about order of the getaddrinfo() results, system
configuration or libc version. It's irrelevant for login(1). We have
to be robust enough to write usable address to log files everywhere.

The solution is to detect IPv4-mapping-to-IPv6 and use IPv4 for utmp.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1296233
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/login-utils/login.c b/login-utils/login.c
index 64b41f4ebf085421c6226e10cb1f8a900a24e3d4..9bc1bd9c466d7c7497653bf570a57aa93c4e9d86 100644 (file)
--- a/login-utils/login.c
+++ b/login-utils/login.c
@@ -1088,8 +1088,15 @@ static void init_remote_info(struct login_context *cxt, char *remotehost)
                } else if (info->ai_family == AF_INET6) {
                        struct sockaddr_in6 *sa =
                                     (struct sockaddr_in6 *) info->ai_addr;
+#ifdef IN6_IS_ADDR_V4MAPPED
+                       if (IN6_IS_ADDR_V4MAPPED(&sa->sin6_addr)) {
+                               const uint8_t *bytes = sa->sin6_addr.s6_addr;
+                               struct in_addr addr = { *(const in_addr_t *) (bytes + 12) };
 
-                       memcpy(cxt->hostaddress, &(sa->sin6_addr), sizeof(sa->sin6_addr));
+                               memcpy(cxt->hostaddress, &addr, sizeof(struct in_addr));
+                       } else
+#endif
+                               memcpy(cxt->hostaddress, &(sa->sin6_addr), sizeof(sa->sin6_addr));
                }
                freeaddrinfo(info);
        }