Patchwork xtables-addons: xt_RAWNAT: skb writable part might not include whole l4 header (ipv4 case).

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Submitter Dmitry Popov
Date May 5, 2013, 6:05 p.m.
Message ID <20130505220504.1a3f2380a1e798b37e628dd1@highloadlab.com>
Download mbox | patch
Permalink /patch/241523/
State Not Applicable
Headers show

Comments

Dmitry Popov - May 5, 2013, 6:05 p.m.
Consider TCP/IPv4 packet with IP options:
sizeof(*iph) + sizeof(struct tcphdr) is not enough to include tcp checksum.
It may hurt if this packet is fragmented.

Therefore we should use iph->ihl * 4 instead of sizeof(*iph).

Signed-off-by: Dmitry Popov <dp@highloadlab.com>
---
 extensions/xt_RAWNAT.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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Dmitry Popov - May 5, 2013, 6:24 p.m.
Also, shouldn't xt_RAWNAT depend on nf_defrag_ipv4 module? 
xt_RAWNAT may work with ip fragments in PREROUTING chain, changing ip payload
(believing it's tcp/udp checksum) in fragment is harmful.
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Patch

diff --git a/extensions/xt_RAWNAT.c b/extensions/xt_RAWNAT.c
index a52e614..858f911 100644
--- a/extensions/xt_RAWNAT.c
+++ b/extensions/xt_RAWNAT.c
@@ -109,7 +109,7 @@  static void rawnat4_update_l4(struct sk_buff *skb, __be32 oldip, __be32 newip)
 
 static unsigned int rawnat4_writable_part(const struct iphdr *iph)
 {
-	unsigned int wlen = sizeof(*iph);
+	unsigned int wlen = iph->ihl * 4;
 
 	switch (iph->protocol) {
 	case IPPROTO_TCP: