netdev - Re: [PATCH v2] rps: fix insufficient bounds checking in store_rps_dev_flow_table

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Date:	Thu, 22 Dec 2011 23:44:51 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] rps: fix insufficient bounds checking in store_rps_dev_flow_table_cnt()

On Dec 22, 2011, at 11:10 PM, Eric Dumazet wrote:
>> -		if (count > 1<<30) {
>> +		if (count > INT_MAX)
>> +			return -EINVAL;
>> +		count = roundup_pow_of_two(count);
>> +		if (count > (ULONG_MAX - sizeof(struct rps_dev_flow_table))
> 
> Oh well, you added a bug here, since count is "unsigned int"
> 
> Why mixing INT_MAX in the previous test and ULONG_MAX here ?

The first check (count > INT_MAX) is used to avoid overflowing
roundup_pow_of_two(count), e.g., when count is 0xffffffff.

The second check is to avoid overflowing the size for vmalloc().
It gives a less restrictive upper bound than using INT_MAX/UINT_MAX
on 64-bit platform.

Why do you think it's a bug there?  I agree using two checks looks
ugly though.

- xi
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