nss_dns: Skip over non-PTR records in the netent code [BZ #19868]

This requires additional checks for the RDATA length and the
availability of record metadata.

2 files changed, 25 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 4c8d7bc6c0..91061fb4cc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2016-03-25  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #19868]
+	* resolv/nss_dns/dns-network.c (getanswer_r): Implement additional
+	DNS packet syntax checks (which were not needed before).  Skip
+	over non-PTR records.
+
 2016-04-27  Florian Weimer  <fweimer@redhat.com>
 
 	* resolv/nss_dns/dns-network.c (offsetof): Remove macro
diff --git a/resolv/nss_dns/dns-network.c b/resolv/nss_dns/dns-network.c
index 99ec7555ab..3ae25c79a7 100644
--- a/resolv/nss_dns/dns-network.c
+++ b/resolv/nss_dns/dns-network.c
@@ -343,10 +343,23 @@ getanswer_r (const querybuf *answer, int anslen, struct netent *result,
       if (n < 0 || res_dnok (bp) == 0)
 	break;
       cp += n;
+
+      if (end_of_message - cp < 10)
+	{
+	  __set_h_errno (NO_RECOVERY);
+	  return NSS_STATUS_UNAVAIL;
+	}
+
       GETSHORT (type, cp);
       GETSHORT (class, cp);
       cp += INT32SZ;		/* TTL */
-      GETSHORT (n, cp);
+      uint16_t rdatalen;
+      GETSHORT (rdatalen, cp);
+      if (end_of_message - cp < rdatalen)
+	{
+	  __set_h_errno (NO_RECOVERY);
+	  return NSS_STATUS_UNAVAIL;
+	}
 
       if (class == C_IN && type == T_PTR)
 	{
@@ -368,7 +381,7 @@ getanswer_r (const querybuf *answer, int anslen, struct netent *result,
 	      cp += n;
 	      return NSS_STATUS_UNAVAIL;
 	    }
-	  cp += n;
+	  cp += rdatalen;
          if (alias_pointer + 2 < &net_data->aliases[MAX_NR_ALIASES])
            {
              *alias_pointer++ = bp;
@@ -379,6 +392,9 @@ getanswer_r (const querybuf *answer, int anslen, struct netent *result,
              ++have_answer;
            }
 	}
+      else
+	/* Skip over unknown record data.  */
+	cp += rdatalen;
     }
 
   if (have_answer)