Changeset c39cd8e for lib/misc.c

Timestamp:

2017-04-02T18:50:49Z (7 years ago)

Author:

Wilmer van der Gaast <wilmer@…>

Children:

df67b48

Parents:

262a82b

Message:

Add reverse_lookup() function which does a more proper (verified) DNS
reverse lookup. (Code copied from OpenSSH instead of redoing it
poorly.)

File:

• lib/misc.c (modified) (1 diff)

lib/misc.c

@@ -549 +549 @@
 }
 
+/* From OpenSSH 7.4p1 canohost.c" */
+char *reverse_lookup(const struct sockaddr *from_, const socklen_t fromlen_)
+{
+        struct sockaddr_storage from;
+        socklen_t fromlen;
+        struct addrinfo hints, *ai, *aitop;
+        char name[NI_MAXHOST], ntop2[NI_MAXHOST];
+        char ntop[INET6_ADDRSTRLEN];
+
+        fromlen = sizeof(from);
+        memset(&from, 0, sizeof(from));
+        memcpy(&from, from_, fromlen_);
+        ipv64_normalise_mapped(&from, &fromlen);
+        if (from.ss_family == AF_INET6) {
+                fromlen = sizeof(struct sockaddr_in6);
+        }
+
+        if (getnameinfo((struct sockaddr *)&from, fromlen, ntop, sizeof(ntop),
+            NULL, 0, NI_NUMERICHOST) != 0) {
+                return NULL;
+        }
+
+        /* Map the IP address to a host name. */
+        if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
+            NULL, 0, NI_NAMEREQD) != 0) {
+                /* Host name not found.  Use ip address. */
+                return g_strdup(ntop);
+        }
+
+        /*
+         * if reverse lookup result looks like a numeric hostname,
+         * someone is trying to trick us by PTR record like following:
+         *      1.1.1.10.in-addr.arpa.  IN PTR  2.3.4.5
+         */
+        memset(&hints, 0, sizeof(hints));
+        hints.ai_socktype = SOCK_DGRAM; /*dummy*/
+        hints.ai_flags = AI_NUMERICHOST;
+        if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
+                freeaddrinfo(ai);
+                return g_strdup(ntop);
+        }
+
+        /* Names are stored in lowercase. */
+        char *tolower = g_utf8_strdown(name, -1);
+        g_snprintf(name, sizeof(name), "%s", tolower);
+        g_free(tolower);
+
+        /*
+         * Map it back to an IP address and check that the given
+         * address actually is an address of this host.  This is
+         * necessary because anyone with access to a name server can
+         * define arbitrary names for an IP address. Mapping from
+         * name to IP address can be trusted better (but can still be
+         * fooled if the intruder has access to the name server of
+         * the domain).
+         */
+        memset(&hints, 0, sizeof(hints));
+        hints.ai_family = from.ss_family;
+        hints.ai_socktype = SOCK_STREAM;
+        if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
+                return g_strdup(ntop);
+        }
+        /* Look for the address from the list of addresses. */
+        for (ai = aitop; ai; ai = ai->ai_next) {
+                if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
+                    sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
+                    (strcmp(ntop, ntop2) == 0))
+                        break;
+        }
+        freeaddrinfo(aitop);
+        /* If we reached the end of the list, the address was not there. */
+        if (ai == NULL) {
+                /* Address not found for the host name. */
+                return g_strdup(ntop);
+        }
+        return g_strdup(name);
+}
+
+void
+ipv64_normalise_mapped(struct sockaddr_storage *addr, socklen_t *len)
+{
+        struct sockaddr_in6 *a6 = (struct sockaddr_in6 *)addr;
+        struct sockaddr_in *a4 = (struct sockaddr_in *)addr;
+        struct in_addr inaddr;
+        u_int16_t port;
+
+        if (addr->ss_family != AF_INET6 ||
+            !IN6_IS_ADDR_V4MAPPED(&a6->sin6_addr))
+                return;
+
+        memcpy(&inaddr, ((char *)&a6->sin6_addr) + 12, sizeof(inaddr));
+        port = a6->sin6_port;
+
+        memset(a4, 0, sizeof(*a4));
+
+        a4->sin_family = AF_INET;
+        *len = sizeof(*a4);
+        memcpy(&a4->sin_addr, &inaddr, sizeof(inaddr));
+        a4->sin_port = port;
+}
+
 char *word_wrap(const char *msg, int line_len)
 {