protocol parsing: check input data stricter

... so that bad length fields aren't blindly accepted

Bug: http://c-ares.haxx.se/mail/c-ares-archive-2013-04/0016.shtml

ares_expand_name.c

@@ -143,7 +143,7 @@ static int name_length(const unsigned char *encoded, const unsigned char *abuf,
   int n = 0, offset, indir = 0;
 
   /* Allow the caller to pass us abuf + alen and have us check for it. */
-  if (encoded == abuf + alen)
+  if (encoded >= abuf + alen)
     return -1;
 
   while (*encoded)

ares_parse_a_reply.c

@@ -136,6 +136,12 @@ int ares_parse_a_reply(const unsigned char *abuf, int alen,
       rr_len = DNS_RR_LEN(aptr);
       rr_ttl = DNS_RR_TTL(aptr);
       aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          free(rr_name);
+          status = ARES_EBADRESP;
+          break;
+        }
 
       if (rr_class == C_IN && rr_type == T_A
           && rr_len == sizeof(struct in_addr)

ares_parse_aaaa_reply.c

@@ -136,6 +136,12 @@ int ares_parse_aaaa_reply(const unsigned char *abuf, int alen,
       rr_len = DNS_RR_LEN(aptr);
       rr_ttl = DNS_RR_TTL(aptr);
       aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          free(rr_name);
+          status = ARES_EBADRESP;
+          break;
+        }
 
       if (rr_class == C_IN && rr_type == T_AAAA
           && rr_len == sizeof(struct ares_in6_addr)

ares_parse_mx_reply.c

@@ -100,6 +100,11 @@ ares_parse_mx_reply (const unsigned char *abuf, int alen,
       rr_class = DNS_RR_CLASS (aptr);
       rr_len = DNS_RR_LEN (aptr);
       aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          status = ARES_EBADRESP;
+          break;
+        }
 
       /* Check if we are really looking at a MX record */
       if (rr_class == C_IN && rr_type == T_MX)

ares_parse_naptr_reply.c

@@ -105,6 +105,11 @@ ares_parse_naptr_reply (const unsigned char *abuf, int alen,
       rr_class = DNS_RR_CLASS (aptr);
       rr_len = DNS_RR_LEN (aptr);
       aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          status = ARES_EBADRESP;
+          break;
+        }
 
       /* Check if we are really looking at a NAPTR record */
       if (rr_class == C_IN && rr_type == T_NAPTR)

ares_parse_ns_reply.c

@@ -105,6 +105,12 @@ int ares_parse_ns_reply( const unsigned char* abuf, int alen,
     rr_class = DNS_RR_CLASS( aptr );
     rr_len = DNS_RR_LEN( aptr );
     aptr += RRFIXEDSZ;
+    if (aptr + rr_len > abuf + alen)
+      {
+        free(rr_name);
+        status = ARES_EBADRESP;
+        break;
+      }
 
     if ( rr_class == C_IN && rr_type == T_NS )
     {

ares_parse_ptr_reply.c

@@ -103,6 +103,12 @@ int ares_parse_ptr_reply(const unsigned char *abuf, int alen, const void *addr,
       rr_class = DNS_RR_CLASS(aptr);
       rr_len = DNS_RR_LEN(aptr);
       aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          free(rr_name);
+          status = ARES_EBADRESP;
+          break;
+        }
 
       if (rr_class == C_IN && rr_type == T_PTR
           && strcasecmp(rr_name, ptrname) == 0)
@@ -203,7 +209,7 @@ int ares_parse_ptr_reply(const unsigned char *abuf, int alen, const void *addr,
       status = ARES_ENOMEM;
     }
   for (i=0 ; i<aliascnt ; i++)
-    if (aliases[i]) 
+    if (aliases[i])
       free(aliases[i]);
   free(aliases);
   if (hostname)

ares_parse_srv_reply.c

@@ -105,6 +105,11 @@ ares_parse_srv_reply (const unsigned char *abuf, int alen,
       rr_class = DNS_RR_CLASS (aptr);
       rr_len = DNS_RR_LEN (aptr);
       aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          status = ARES_EBADRESP;
+          break;
+        }
 
       /* Check if we are really looking at a SRV record */
       if (rr_class == C_IN && rr_type == T_SRV)

ares_parse_txt_reply.c

@@ -106,6 +106,11 @@ ares_parse_txt_reply (const unsigned char *abuf, int alen,
       rr_class = DNS_RR_CLASS (aptr);
       rr_len = DNS_RR_LEN (aptr);
       aptr += RRFIXEDSZ;
+      if (aptr + rr_len > abuf + alen)
+        {
+          status = ARES_EBADRESP;
+          break;
+        }
 
       /* Check if we are really looking at a TXT record */
       if (rr_class == C_IN && rr_type == T_TXT)
@@ -144,6 +149,12 @@ ares_parse_txt_reply (const unsigned char *abuf, int alen,
               strptr += substr_len + 1;
             }
 
+          if (strptr != (aptr + rr_len))
+            {
+              status = ARES_EBADRESP;
+              break;
+            }
+
           /* Including null byte */
           txt_curr->txt = malloc (txt_curr->length + 1);
           if (txt_curr->txt == NULL)