Subject: Re: [PATCH, take2] netfilter : struct xt_table_info diet

From: Patrick McHardy <[email-masked]>
Date: Thu, 15 Nov 2007 16:58:43 +0100

Eric Dumazet wrote:
> On Thu, 15 Nov 2007 13:41:54 +0100
> Patrick McHardy <[email-masked]> wrote:
> 
>>> +#define XT_TABLE_INFO_SZ (offsetof(struct xt_table_info, entries) \
>>> +			  + nr_cpu_ids * sizeof(char *))
>>
>>>  	/* overflow check */
>>> -	if (tmp.size >= (INT_MAX - sizeof(struct xt_table_info)) / NR_CPUS -
>>> -			SMP_CACHE_BYTES)
>>> +	if (tmp.size >= INT_MAX / num_possible_cpus())
>>>  		return -ENOMEM;
>> We need to make sure offsetof(struct xt_table_info, entries) +
>> nr_cpu_ids * sizeof(char *) doesn't overflow, so why doesn't it
>> use nr_cpu_ids here as well?
>>
> 
> nr_cpu_ids is <= NR_CPUS, so XT_TABLE_INFO_SZ cannot overflow

Yes, but nr_cpu_ids is >= num_possible_cpus, which is what we're
using with your patch.

> The 'overflow check' we do here is in fact not very usefull now
> that we dont need to multiply tmp.size by NR_CPUS and potentially
> overflow the result.
> 
> We can delete the test, because kmalloc()/vmalloc() will probably
> fail gracefully if we ask too much memory.

You're right, I'll remove it. Thanks.