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netfilter: synproxy: fix BUG_ON triggered by corrupt TCP packets 

TCP packets hitting the SYN proxy through the SYNPROXY target are not
validated by TCP conntrack. When th->doff is below 5, an underflow happens
when calculating the options length, causing skb_header_pointer() to
return NULL and triggering the BUG_ON().

Handle this case gracefully by checking for NULL instead of using BUG_ON().

Reported-by: Martin Topholm <mph@one.com>
Tested-by: Martin Topholm <mph@one.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Patrick McHardy 2013-09-30 08:51:46 +01:00 committed by Pablo Neira Ayuso
parent d1ee4fea0b
commit f4a87e7bd2
4 changed files with 22 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/net/netfilter/nf_conntrack_synproxy.h
View File

@ -56,7 +56,7 @@ struct synproxy_options {
struct tcphdr;
struct xt_synproxy_info;
extern void synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
extern bool synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
const struct tcphdr *th,
struct synproxy_options *opts);
extern unsigned int synproxy_options_size(const struct synproxy_options *opts);

10
net/ipv4/netfilter/ipt_SYNPROXY.c
View File

@ -267,7 +267,8 @@ synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
if (th == NULL)
return NF_DROP;
synproxy_parse_options(skb, par->thoff, th, &opts);
if (!synproxy_parse_options(skb, par->thoff, th, &opts))
return NF_DROP;
if (th->syn && !(th->ack || th->fin || th->rst)) {
/* Initial SYN from client */
@ -350,7 +351,8 @@ static unsigned int ipv4_synproxy_hook(unsigned int hooknum,
/* fall through */
case TCP_CONNTRACK_SYN_SENT:
synproxy_parse_options(skb, thoff, th, &opts);
if (!synproxy_parse_options(skb, thoff, th, &opts))
return NF_DROP;
if (!th->syn && th->ack &&
CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
@ -373,7 +375,9 @@ static unsigned int ipv4_synproxy_hook(unsigned int hooknum,
if (!th->syn || !th->ack)
break;
synproxy_parse_options(skb, thoff, th, &opts);
if (!synproxy_parse_options(skb, thoff, th, &opts))
return NF_DROP;
if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
synproxy->tsoff = opts.tsval - synproxy->its;

10
net/ipv6/netfilter/ip6t_SYNPROXY.c
View File

@ -282,7 +282,8 @@ synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
if (th == NULL)
return NF_DROP;
synproxy_parse_options(skb, par->thoff, th, &opts);
if (!synproxy_parse_options(skb, par->thoff, th, &opts))
return NF_DROP;
if (th->syn && !(th->ack || th->fin || th->rst)) {
/* Initial SYN from client */
@ -372,7 +373,8 @@ static unsigned int ipv6_synproxy_hook(unsigned int hooknum,
/* fall through */
case TCP_CONNTRACK_SYN_SENT:
synproxy_parse_options(skb, thoff, th, &opts);
if (!synproxy_parse_options(skb, thoff, th, &opts))
return NF_DROP;
if (!th->syn && th->ack &&
CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
@ -395,7 +397,9 @@ static unsigned int ipv6_synproxy_hook(unsigned int hooknum,
if (!th->syn || !th->ack)
break;
synproxy_parse_options(skb, thoff, th, &opts);
if (!synproxy_parse_options(skb, thoff, th, &opts))
return NF_DROP;
if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
synproxy->tsoff = opts.tsval - synproxy->its;

12
net/netfilter/nf_synproxy_core.c
View File

@ -24,7 +24,7 @@
int synproxy_net_id;
EXPORT_SYMBOL_GPL(synproxy_net_id);
void
bool
synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
const struct tcphdr *th, struct synproxy_options *opts)
{
@ -32,7 +32,8 @@ synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
u8 buf[40], *ptr;
ptr = skb_header_pointer(skb, doff + sizeof(*th), length, buf);
BUG_ON(ptr == NULL);
if (ptr == NULL)
return false;
opts->options = 0;
while (length > 0) {
@ -41,16 +42,16 @@ synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
switch (opcode) {
case TCPOPT_EOL:
return;
return true;
case TCPOPT_NOP:
length--;
continue;
default:
opsize = *ptr++;
if (opsize < 2)
return;
return true;
if (opsize > length)
return;
return true;
switch (opcode) {
case TCPOPT_MSS:
@ -84,6 +85,7 @@ synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
length -= opsize;
}
}
return true;
}
EXPORT_SYMBOL_GPL(synproxy_parse_options);