lkml.org 
[lkml]   [2011]   [Nov]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] comedi: integer overflow in do_insnlist_ioctl()
On 11/23/2011 05:06 PM, Ian Abbott wrote:
> On 2011-11-23 14:50, Dan Carpenter wrote:
>> On Wed, Nov 23, 2011 at 08:59:52AM -0500, Xi Wang wrote:
>>> Thanks for the pointer. However you cannot do the overflow check using
>>>
>>> if (sizeof(struct comedi_insn) * insnlist.n_insns <
>>> insnlist.n_insns)
>>>
>>> Let's assume 32-bit system, sizeof(struct comedi_insn) = 32, and
>>> insnlist.n_insns = 0x7fffffff.
>>>
>>> Note that 32 * 0x7fffffff = 0xffffffe0 overflows but bypasses your
>>> check.
>>>
>>
>> Argh... You're right, my check is wrong. What I like about my patch
>> though is that it doesn't introduce an arbitrary limit. Could you
>> redo your check without the MAX_INSNS?
>
> Could use something like:
>
> if (insnlist.n_insns <= ULONG_MAX / sizeof(struct comedi_insn))
> insns =
> kmalloc(sizeof(struct comedi_insn) * insnlist.n_insns,
> GFP_KERNEL);
> if (!insns)
> ...
>
> (note that insns is initialized to NULL).
>

Just use kcalloc, it will do the right thing for you.

- Lars


\
 
 \ /
  Last update: 2011-11-23 22:43    [W:0.085 / U:0.188 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site