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

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Date:	Fri, 23 Dec 2011 05:53:27 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Xi Wang <xi.wang@...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()

Le jeudi 22 décembre 2011 à 23:44 -0500, Xi Wang a écrit :
> 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

All I wanted to say is that while mixing INT_MAX/ULONG_MAX, you could
have spotted the other bug in the code :

unsigned int count;

count = simple_strtoul(buf, &endp, 0);



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