ipv6/exthdrs: strict Pad1 and PadN check
The following tightens the padding check from commit
c1412fce7eccae62b4de22494f6ab3ff8a90c0c6 :
* Take into account combinations of consecutive Pad1 and PadN.
* Catch the corner case of when only padding is present in the
header, when the extention header length is 0 (i.e., 8 bytes).
In this case, the header would have exactly 6 bytes of padding:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Next Header : Hdr Ext Len=0 : :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
: Padding (Pad1 or PadN) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Signed-off-by: Eldad Zack <eldad@fogrefinery.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 50ec95f..6447dc4 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -144,6 +144,7 @@
const unsigned char *nh = skb_network_header(skb);
int off = skb_network_header_len(skb);
int len = (skb_transport_header(skb)[1] + 1) << 3;
+ int padlen = 0;
if (skb_transport_offset(skb) + len > skb_headlen(skb))
goto bad;
@@ -158,6 +159,9 @@
switch (nh[off]) {
case IPV6_TLV_PAD1:
optlen = 1;
+ padlen++;
+ if (padlen > 7)
+ goto bad;
break;
case IPV6_TLV_PADN:
@@ -166,7 +170,8 @@
* of 8. 7 is therefore the highest valid value.
* See also RFC 4942, Section 2.1.9.5.
*/
- if (optlen > 7)
+ padlen += optlen;
+ if (padlen > 7)
goto bad;
/* RFC 4942 recommends receiving hosts to
* actively check PadN payload to contain
@@ -195,11 +200,19 @@
if (ip6_tlvopt_unknown(skb, off) == 0)
return false;
}
+ padlen = 0;
break;
}
off += optlen;
len -= optlen;
}
+ /* This case will not be caught by above check since its padding
+ * length is smaller than 7:
+ * 1 byte NH + 1 byte Length + 6 bytes Padding
+ */
+ if ((padlen == 6) && ((off - skb_network_header_len(skb)) == 8))
+ goto bad;
+
if (len == 0)
return true;
bad: