Re: [PATCH nf 2/5] netfilter: nfnl_cthelper: fix incorrect helper->expect_class_max

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Sun, Mar 19, 2017 at 10:35:59PM +0800, Liping Zhang wrote:
> From: Liping Zhang <zlpnobody@gmail.com>
> 
> The helper->expect_class_max must be set to the total number of
> expect_policy minus 1, since we will use the statement "if (class >
> helper->expect_class_max)" to validate the CTA_EXPECT_CLASS attr in
> ctnetlink_alloc_expect.
> 
> So for compatibility, set the helper->expect_class_max to the
> NFCTH_POLICY_SET_NUM attr's value minus 1.
> 
> Also: it's invalid when the NFCTH_POLICY_SET_NUM attr's value is zero.
> 1. this will result "expect_policy = kzalloc(0, GFP_KERNEL);";
> 2. we cannot set the helper->expect_class_max to a proper value.
> 
> So if nla_get_be32(tb[NFCTH_POLICY_SET_NUM]) is zero, report -EINVAL to
> the userspace.
> 
> Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
> ---
>  net/netfilter/nfnetlink_cthelper.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
> index 9c24301..cc70dd5 100644
> --- a/net/netfilter/nfnetlink_cthelper.c
> +++ b/net/netfilter/nfnetlink_cthelper.c
> @@ -161,6 +161,7 @@ nfnl_cthelper_parse_expect_policy(struct nf_conntrack_helper *helper,
>  	int i, ret;
>  	struct nf_conntrack_expect_policy *expect_policy;
>  	struct nlattr *tb[NFCTH_POLICY_SET_MAX+1];
> +	unsigned int class_max;
>  
>  	ret = nla_parse_nested(tb, NFCTH_POLICY_SET_MAX, attr,
>  			       nfnl_cthelper_expect_policy_set);
> @@ -170,19 +171,18 @@ nfnl_cthelper_parse_expect_policy(struct nf_conntrack_helper *helper,
>  	if (!tb[NFCTH_POLICY_SET_NUM])
>  		return -EINVAL;
>  
> -	helper->expect_class_max =
> -		ntohl(nla_get_be32(tb[NFCTH_POLICY_SET_NUM]));
> -
> -	if (helper->expect_class_max != 0 &&
> -	    helper->expect_class_max > NF_CT_MAX_EXPECT_CLASSES)
> +	class_max = ntohl(nla_get_be32(tb[NFCTH_POLICY_SET_NUM]));
> +	if (class_max == 0)
> +		return -EINVAL;

I think this patch is just fixing up this case. We should always
provide a policy for the expectation.

> +	if (class_max > NF_CT_MAX_EXPECT_CLASSES)
>  		return -EOVERFLOW;
>  
>  	expect_policy = kzalloc(sizeof(struct nf_conntrack_expect_policy) *
> -				helper->expect_class_max, GFP_KERNEL);
> +				class_max, GFP_KERNEL);
>  	if (expect_policy == NULL)
>  		return -ENOMEM;
>  
> -	for (i=0; i<helper->expect_class_max; i++) {
> +	for (i = 0; i < class_max; i++) {
>  		if (!tb[NFCTH_POLICY_SET+i])
>  			goto err;
>  
> @@ -191,6 +191,8 @@ nfnl_cthelper_parse_expect_policy(struct nf_conntrack_helper *helper,
>  		if (ret < 0)
>  			goto err;
>  	}
> +
> +	helper->expect_class_max = class_max - 1;

Why - 1 ?

class_max represents the array size, you can just keep this code the
way it is.

>  	helper->expect_policy = expect_policy;
>  	return 0;
>  err:
> @@ -375,10 +377,10 @@ nfnl_cthelper_dump_policy(struct sk_buff *skb,
>  		goto nla_put_failure;
>  
>  	if (nla_put_be32(skb, NFCTH_POLICY_SET_NUM,
> -			 htonl(helper->expect_class_max)))
> +			 htonl(helper->expect_class_max + 1)))
>  		goto nla_put_failure;
>  
> -	for (i=0; i<helper->expect_class_max; i++) {
> +	for (i = 0; i < helper->expect_class_max + 1; i++) {
>  		nest_parms2 = nla_nest_start(skb,
>  				(NFCTH_POLICY_SET+i) | NLA_F_NESTED);
>  		if (nest_parms2 == NULL)
> -- 
> 2.5.5
> 
>