nss_dns: Validate RDATA length against packet length [BZ #19830]

In _nss_dns_getcanonname_r, a check for the availability of RR metadata
was missing as well.

3 files changed, 36 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 954c95f9a9..081994cf6f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
 2016-04-27  Florian Weimer  <fweimer@redhat.com>
 
+	[BZ #19830]
+	* resolv/nss_dns/dns-host.c (getanswer_r): Check RDATA length.
+	(gaih_getanswer_slice): Likewise.
+	* resolv/nss_dns/dns-canon.c (_nss_dns_getcanonname_r): Likewise.
+	Also check for availability of RR metadata.
+
+2016-04-27  Florian Weimer  <fweimer@redhat.com>
+
 	[BZ #19825]
 	* resolv/res_send.c (send_vc): Remove early *resplen2
 	initialization.  Set *resplen2 on socket error.  Call
diff --git a/resolv/nss_dns/dns-canon.c b/resolv/nss_dns/dns-canon.c
index fd73f19984..072104f21c 100644
--- a/resolv/nss_dns/dns-canon.c
+++ b/resolv/nss_dns/dns-canon.c
@@ -103,6 +103,11 @@ _nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
 
 	      ptr += s;
 
+	      /* Check that there are enough bytes for the RR
+		 metadata.  */
+	      if (endptr - ptr < 10)
+		goto unavail;
+
 	      /* Check whether type and class match.  */
 	      uint_fast16_t type;
 	      NS_GET16 (type, ptr);
@@ -137,11 +142,16 @@ _nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
 	      if (__ns_get16 (ptr) != ns_c_in)
 		goto unavail;
 
-	      /* Also skip over the TTL.  */
+	      /* Also skip over class and TTL.  */
 	      ptr += sizeof (uint16_t) + sizeof (uint32_t);
 
-	      /* Skip over the data length and data.  */
-	      ptr += sizeof (uint16_t) + __ns_get16 (ptr);
+	      /* Skip over RDATA length and RDATA itself.  */
+	      uint16_t rdatalen = __ns_get16 (ptr);
+	      ptr += sizeof (uint16_t);
+	      /* Not enough room for RDATA.  */
+	      if (endptr - ptr < rdatalen)
+		goto unavail;
+	      ptr += rdatalen;
 	    }
 	}
 
diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index 8599f4c6a6..4bb0e6268a 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -751,6 +751,14 @@ getanswer_r (const querybuf *answer, int anslen, const char *qname, int qtype,
       cp += INT32SZ;			/* TTL */
       n = __ns_get16 (cp);
       cp += INT16SZ;			/* len */
+
+      if (end_of_message - cp < n)
+	{
+	  /* RDATA extends beyond the end of the packet.  */
+	  ++had_error;
+	  continue;
+	}
+
       if (__glibc_unlikely (class != C_IN))
 	{
 	  /* XXX - debug? syslog? */
@@ -1077,6 +1085,13 @@ gaih_getanswer_slice (const querybuf *answer, int anslen, const char *qname,
       n = __ns_get16 (cp);
       cp += INT16SZ;			/* len */
 
+      if (end_of_message - cp < n)
+	{
+	  /* RDATA extends beyond the end of the packet.  */
+	  ++had_error;
+	  continue;
+	}
+
       if (class != C_IN)
 	{
 	  cp += n;