net/ipv6/exthdrs.c: Strict PadN option checking

Added strict checking of PadN, as PadN can be used to increase header size and thus push the protocol header into the 2nd fragment. PadN is used to align the options within the Hop-by-Hop or Destination Options header to 64-bit boundaries. The maximum valid size is thus 7 bytes. RFC 4942 recommends to actively check the "payload" itself and ensure that it contains only zeroes. See also RFC 4942 section 2.1.9.5. Signed-off-by: Eldad Zack <[email protected]> Signed-off-by: David S. Miller <[email protected]>
jadonk · Apr 12, 2012 · c1412fc · c1412fc
1 parent 46ba5b2
commit c1412fc
Showing 1 changed file with 16 additions and 0 deletions.
diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
@@ -153,13 +153,29 @@ static int ip6_parse_tlv(struct tlvtype_proc *procs, struct sk_buff *skb)
 
 	while (len > 0) {
 		int optlen = nh[off + 1] + 2;
+		int i;
 
 		switch (nh[off]) {
 		case IPV6_TLV_PAD0:
 			optlen = 1;
 			break;
 
 		case IPV6_TLV_PADN:
+			/* RFC 2460 states that the purpose of PadN is
+			 * to align the containing header to multiples
+			 * of 8. 7 is therefore the highest valid value.
+			 * See also RFC 4942, Section 2.1.9.5.
+			 */
+			if (optlen > 7)
+				goto bad;
+			/* RFC 4942 recommends receiving hosts to
+			 * actively check PadN payload to contain
+			 * only zeroes.
+			 */
+			for (i = 2; i < optlen; i++) {
+				if (nh[off + i] != 0)
+					goto bad;
+			}
 			break;
 
 		default: /* Other TLV code so scan list */