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

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

[Florian Weimer]

[-- Attachment #1: Type: text/plain, Size: 102 bytes --]

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

Florian

[-- Attachment #2: 0001-nss_dns-Validate-RDATA-length-against-packet-length-.patch --]
[-- Type: text/x-patch, Size: 2372 bytes --]

2016-03-25  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.

diff --git a/resolv/nss_dns/dns-canon.c b/resolv/nss_dns/dns-canon.c
index 27255fd..5c5c6db 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 8599f4c..4bb0e62 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;

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

[Florian Weimer]

On 03/25/2016 07:57 PM, Florian Weimer wrote:
>
> 2016-03-25  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.

I have pushed this.

Thanks,
Florian