[PATCH 3.2 63/79] netfilter: xt_TCPMSS: Fix missing fragmentation handling

Ben Hutchings
2018-02-11T04:33:41Z

From: Phil Oester <kernel@linuxace.com>

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@linuxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
[bwh: Backported to 3.2: Change parameters for tcpmss_mangle_packet() as
done upstream in commit 70d19f805f8c "netfilter: xt_TCPMSS: Fix IPv6 default
MSS too"]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -44,17 +44,22 @@ optlen(const u_int8_t *opt, unsigned int

static int
tcpmss_mangle_packet(struct sk_buff *skb,
- const struct xt_tcpmss_info *info,
+ const struct xt_action_param *par,
unsigned int in_mtu,
unsigned int tcphoff,
unsigned int minlen)
{
+ const struct xt_tcpmss_info *info = par->targinfo;
struct tcphdr *tcph;
unsigned int tcplen, i;
__be16 oldval;
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;

@@ -183,7 +188,7 @@ tcpmss_tg4(struct sk_buff *skb, const st
__be16 newlen;
int ret;

- ret = tcpmss_mangle_packet(skb, par->targinfo,
+ ret = tcpmss_mangle_packet(skb, par,
tcpmss_reverse_mtu(skb, PF_INET),
iph->ihl * 4,
sizeof(*iph) + sizeof(struct tcphdr));
@@ -211,7 +216,7 @@ tcpmss_tg6(struct sk_buff *skb, const st
tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr);
if (tcphoff < 0)
return NF_DROP;
- ret = tcpmss_mangle_packet(skb, par->targinfo,
+ ret = tcpmss_mangle_packet(skb, par,
tcpmss_reverse_mtu(skb, PF_INET6),
tcphoff,
sizeof(*ipv6h) + sizeof(struct tcphdr));