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@xxxxxxx>
Tested-by: Martin Topholm <mph@xxxxxxx>
Signed-off-by: Patrick McHardy <kaber@xxxxxxxxx>
---
include/net/netfilter/nf_conntrack_synproxy.h | 2 +-
net/ipv4/netfilter/ipt_SYNPROXY.c | 10 +++++++---
net/ipv6/netfilter/ip6t_SYNPROXY.c | 10 +++++++---
net/netfilter/nf_synproxy_core.c | 12 +++++++-----
4 files changed, 22 insertions(+), 12 deletions(-)
diff --git a/include/net/netfilter/nf_conntrack_synproxy.h b/include/net/netfilter/nf_conntrack_synproxy.h
index 806f54a..f572f31 100644
--- a/include/net/netfilter/nf_conntrack_synproxy.h
+++ b/include/net/netfilter/nf_conntrack_synproxy.h
@@ -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);
diff --git a/net/ipv4/netfilter/ipt_SYNPROXY.c b/net/ipv4/netfilter/ipt_SYNPROXY.c
index 67e17dc..b6346bf 100644
--- a/net/ipv4/netfilter/ipt_SYNPROXY.c
+++ b/net/ipv4/netfilter/ipt_SYNPROXY.c
@@ -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;
diff --git a/net/ipv6/netfilter/ip6t_SYNPROXY.c b/net/ipv6/netfilter/ip6t_SYNPROXY.c
index 19cfea8..2748b04 100644
--- a/net/ipv6/netfilter/ip6t_SYNPROXY.c
+++ b/net/ipv6/netfilter/ip6t_SYNPROXY.c
@@ -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;
diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index 6fd967c..cdf4567 100644
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -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);
--
1.8.3.1
--
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