nss_dns: Check address length before creating addrinfo result [BZ #19831]

Previously, we allocated room in the result space before the check,
leaving uninitialized data there in case the check failed.

This also consolidates the behavior between single (A or AAAA) and
dual (A and AAAA in parallel) queries.  Single queries checked
the record length against the QTYPE, not the RRTYPE.

(cherry picked from commit 5e0c421cc07e2d06945b863ed3bb92395472705d)

2 files changed, 47 insertions, 20 deletions

diff --git a/ChangeLog b/ChangeLog
index adc9b65132..1fef1d5204 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
 2016-04-27  Florian Weimer  <fweimer@redhat.com>
 
+	[BZ #19831]
+	* resolv/nss_dns/dns-host.c (rrtype_to_rdata_length): New
+	function.
+	(getanswer_r): Check RDATA length against RRTYPE and QTYPE.
+	(gaih_getanswer_slice): Check RDATA length against RRTYPE.
+
+2016-04-27  Florian Weimer  <fweimer@redhat.com>
+
 	[BZ #19862]
 	* resolv/nss_dns/dns-host.c (AskedForGot): Remove.
 	(getanswer_r): Do not call syslog.
diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index fb1d21cad7..403a005812 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -134,6 +134,22 @@ extern enum nss_status _nss_dns_gethostbyname3_r (const char *name, int af,
 						  char **canonp);
 hidden_proto (_nss_dns_gethostbyname3_r)
 
+/* Return the expected RDATA length for an address record type (A or
+   AAAA).  */
+static int
+rrtype_to_rdata_length (int type)
+{
+  switch (type)
+    {
+    case T_A:
+      return INADDRSZ;
+    case T_AAAA:
+      return IN6ADDRSZ;
+    default:
+      return -1;
+    }
+}
+
 enum nss_status
 _nss_dns_gethostbyname3_r (const char *name, int af, struct hostent *result,
 			   char *buffer, size_t buflen, int *errnop,
@@ -888,6 +904,15 @@ getanswer_r (const querybuf *answer, int anslen, const char *qname, int qtype,
 	      cp += n;
 	      continue;			/* XXX - had_error++ ? */
 	    }
+
+	  /* Stop parsing at a record whose length is incorrect.  */
+	  if (n != rrtype_to_rdata_length (type))
+	    {
+	      ++had_error;
+	      break;
+	    }
+
+	  /* Skip records of the wrong type.  */
 	  if (n != result->h_length)
 	    {
 	      cp += n;
@@ -1124,25 +1149,25 @@ gaih_getanswer_slice (const querybuf *answer, int anslen, const char *qname,
 	    }
 	  continue;
 	}
-#if 1
-      // We should not see any types other than those explicitly listed
-      // below.  Some types sent by server seem missing, though.  Just
-      // collect the data for now.
-      if (__glibc_unlikely (type != T_A && type != T_AAAA))
-#else
-      if (__builtin_expect (type == T_SIG, 0)
-	  || __builtin_expect (type == T_KEY, 0)
-	  || __builtin_expect (type == T_NXT, 0)
-	  || __builtin_expect (type == T_PTR, 0)
-	  || __builtin_expect (type == T_DNAME, 0))
-#endif
+
+      /* Stop parsing if we encounter a record with incorrect RDATA
+	 length.  */
+      if (type == T_A || type == T_AAAA)
+	{
+	  if (n != rrtype_to_rdata_length (type))
+	    {
+	      ++had_error;
+	      continue;
+	    }
+	}
+      else
 	{
+	  /* Skip unknown records.  */
 	  cp += n;
 	  continue;
 	}
-      if (type != T_A && type != T_AAAA)
-	abort ();
 
+      assert (type == T_A || type == T_AAAA);
       if (*pat == NULL)
 	{
 	  uintptr_t pad = (-(uintptr_t) buffer
@@ -1176,12 +1201,6 @@ gaih_getanswer_slice (const querybuf *answer, int anslen, const char *qname,
 	}
 
       (*pat)->family = type == T_A ? AF_INET : AF_INET6;
-      if (__builtin_expect ((type == T_A && n != INADDRSZ)
-			    || (type == T_AAAA && n != IN6ADDRSZ), 0))
-	{
-	  ++had_error;
-	  continue;
-	}
       memcpy ((*pat)->addr, cp, n);
       cp += n;
       (*pat)->scopeid = 0;