2012-05-20 11:59:56

by Eldad Zack

Subject: [PATCH] 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 <[email protected]>
---
net/ipv6/exthdrs.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

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 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
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 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
switch (nh[off]) {
case IPV6_TLV_PAD1:
optlen = 1;
+ padlen++;
+ if (padlen > 7)
+ goto bad;
break;

case IPV6_TLV_PADN:
@@ -166,7 +170,8 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
* 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 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
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:
--
1.7.10

2012-05-20 21:02:38

by David Miller

Subject: Re: [PATCH] ipv6/exthdrs: strict Pad1 and PadN check

From: Eldad Zack <[email protected]>
Date: Sun, 20 May 2012 13:59:33 +0200

> 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 <[email protected]>

Applied to net-next, thanks a lot.