Gopalakrishnan Raman wrote:
Hi
I'm using 2.6.11.7 and debugging why my ESP tunnel mode does
not work between two 2.6 machines one of which is behind a NAT.
I'm using tcpdump to capture NAT-T packets on one of the hosts
and using espdecrypt (http://www.cs.rpi.edu/~flemej/freebsd/espdecrypt/)
to see it in the clear.
Turns out, tcpdump will display an incoming NAT-T packet after it
has been mangled by udp_encap_rcv(). udp_encap_rcv() changes the
protocol field in the IP hdr to ESP from UDP and also moves other
bytes in the sk_buff data area.
The problem is that packet_rcv() calls skb_clone() which is the
right thing to do in all cases except when the data portion of the
incoming skb is being modified in place. I replaced it with a pskb_copy()
in the case when the packet is likely to be NAT-T or ESP. The patch
for this follows the end of this mail and seems to work quite well.
Note that af_packet.c is the right place for the ESP/NAT-T check.
Can't do it in ESP or UDP code because we can't tell if these packets
are also being captured by tcpdump/ethereal.
Herbert already fixed it with this patch.
[IPSEC]: COW skb header in UDP decap
The following patch just makes the header part of the skb writeable.
This is needed since we modify the IP headers just a few lines below.
Signed-off-by: Herbert Xu <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
---
commit 4d78b6c78ae6d87e4c1c8072f42efa716f04afb9
tree e04f156e8d74c28b925bf53e62d3e4b424a6ffb7
parent c7f905f0f6d49ed8c1aa4566c31f0383a0ba0c9d
author Herbert Xu <[email protected]> Tue, 19 Apr 2005 22:48:59 -0700
committer David S. Miller <[email protected]> Tue, 19 Apr 2005 22:48:59 -0700
net/ipv4/udp.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -955,6 +955,8 @@ static int udp_encap_rcv(struct sock * s
* header and optional ESP marker bytes) and then modify the
* protocol to ESP, and then call into the transform receiver.
*/
+ if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+ return 0;
/* Now we can update and verify the packet length... */
iph = skb->nh.iph;
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