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

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Date:	Fri, 23 Dec 2011 06:16:30 +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 vendredi 23 décembre 2011 à 00:10 -0500, Xi Wang a écrit :
> On Dec 22, 2011, at 11:53 PM, Eric Dumazet wrote:
> > 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);
> 
> Are you suggesting to change the type of "count" to unsigned long?
> That seems like a separate issue from the bounds checking part.
> 
> I don't see the possible 32-bit truncation here is a serious issue though.
> The user could even echo "128abc" into rps_flow_cnt and simple_strtoul()
> would be happy to pick 128.
> 

32 bit truncation _is_ a bound checking problem too.

Really, mixing INT_MAX / ULONG_MAX is ugly, this should had ring a bell
when writing such hard to read code.

You cannot claim to give more range to 64bit platform, yet not spotting
the 32bit truncation issue.

When fixing a bug, its always a good thing to look things around, and
try to check the whole function.



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