Re: [PATCH 1/1] netfilter: h323: avoid potential attack

[Eric Dumazet]

On Wed, 2016-01-27 at 22:40 +0800, Zhouyi Zhou wrote:
> From: Zhouyi Zhou <yizhouzhou@xxxxxxxxx>
> 
> I think hackers chould build a malicious h323 packet to overflow
> the pointer p which will panic during the memcpy(addr, p, len)
> 
> For example, he may fabricate a very large taddr->ipAddress.ip; 
> 
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@xxxxxxxxx>
> ---
>  net/netfilter/nf_conntrack_h323_main.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/netfilter/nf_conntrack_h323_main.c b/net/netfilter/nf_conntrack_h323_main.c
> index 9511af0..3b3dd8c 100644
> --- a/net/netfilter/nf_conntrack_h323_main.c
> +++ b/net/netfilter/nf_conntrack_h323_main.c
> @@ -110,6 +110,10 @@ int (*nat_q931_hook) (struct sk_buff *skb,
>  
>  static DEFINE_SPINLOCK(nf_h323_lock);
>  static char *h323_buffer;
> +#define CHECK_BOUND(p, n) do {					\
> +		if (((p - h323_buffer) + n) > 65536)		\
> +			return 0;				\
> +} while (0)
>  


Do not add 'return X;' or 'goto something;' in macros please.

Even referring to 'h323_buffer' is not nice, and of course 65536 is
another 'magic' value.

Even if h323_buffer was allocated to hold 65536 bytes, the various
skb_header_pointer() calls only populated a part of it.

I understand there is a bad precedent in
net/netfilter/nf_conntrack_h323_asn1.c, but it is not a good reason.

Anyway, if the issue is real, you do not take into account the 2 extra
bytes for the port.

memcpy(port, p + len, sizeof(__be16));