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Diffstat (limited to 'net/netfilter/xt_TCPMSS.c')
-rw-r--r--net/netfilter/xt_TCPMSS.c23
1 files changed, 20 insertions, 3 deletions
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index a75240f0d42b..7011c71646f0 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -45,17 +45,22 @@ optlen(const u_int8_t *opt, unsigned int offset)
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;
@@ -125,6 +130,18 @@ tcpmss_mangle_packet(struct sk_buff *skb,
skb_put(skb, TCPOLEN_MSS);
+ /*
+ * IPv4: RFC 1122 states "If an MSS option is not received at
+ * connection setup, TCP MUST assume a default send MSS of 536".
+ * IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
+ * length IPv6 header of 60, ergo the default MSS value is 1220
+ * Since no MSS was provided, we must use the default values
+ */
+ if (par->family == NFPROTO_IPV4)
+ newmss = min(newmss, (u16)536);
+ else
+ newmss = min(newmss, (u16)1220);
+
opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
@@ -182,7 +199,7 @@ tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
__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 +228,7 @@ tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
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));