[PATCH 49/98] netfilter: xt_TCPMSS: Fix missing fragmentation handling

[Luis Henriques]

3.5.7.17 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Phil Oester <kernel@xxxxxxxxxxxx>

commit b396966c4688522863572927cb30aa874b3ec504 upstream.

Similar to commit bc6bcb59 ("netfilter: xt_TCPOPTSTRIP: fix
possible mangling beyond packet boundary"), add safe fragment
handling to xt_TCPMSS.

Signed-off-by: Phil Oester <kernel@xxxxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 net/netfilter/xt_TCPMSS.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 4960b66..a77d786 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -55,6 +55,10 @@ tcpmss_mangle_packet(struct sk_buff *skb,
 	u16 newmss;
 	u8 *opt;
 
+	/* This is a fragment, no TCP header is available */
+	if (par->fragoff != 0)
+		return XT_CONTINUE;
+
 	if (!skb_make_writable(skb, skb->len))
 		return -1;
 
-- 
1.8.1.2

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