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
@@ -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);