netfilter: xt_TCPMSS: Fix missing fragmentation handling

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@linuxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 6640a224f9fb..7011c71646f0 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -57,6 +57,10 @@ 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;