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Subject[PATCH] AH4: Update IPv4 options handling to conform to RFC 4302.
In testing our ESP/AH offload hardware, I discovered an issue with how AH
handles mutable fields in IPv4. RFC 4302 (AH) states the following on the

For IPv4, the entire option is viewed as a unit; so even
though the type and length fields within most options are immutable
in transit, if an option is classified as mutable, the entire option
is zeroed for ICV computation purposes.

The current implementation does not zero the type and length fields, resulting
in authentication failures when communicating with hosts that do (i.e. FreeBSD).

I have tested record route and timestamp options (ping -R and ping -T) on a
small network involving Windows XP, FreeBSD 6.2, and Linux hosts, with one
router. In the presence of these options, the FreeBSD and Linux hosts (with
the patch or with the hardware) can communicate. The Windows XP host simply
fails to accept these packets with or without the patch.

I have also been trying to test source routing options (using traceroute -g),
but haven't had much luck getting this option to work *without* AH, let alone

Signed-off-by: Nick Bowler <>
net/ipv4/ah4.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
index 7a23e59..39f6211 100644
--- a/net/ipv4/ah4.c
+++ b/net/ipv4/ah4.c
@@ -46,7 +46,7 @@ static int ip_clear_mutable_options(struct iphdr *iph, __be32 *daddr)
memcpy(daddr, optptr+optlen-4, 4);
/* Fall through */
- memset(optptr+2, 0, optlen-2);
+ memset(optptr, 0, optlen);
l -= optlen;
optptr += optlen;
Nick Bowler, Elliptic Semiconductor (

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