Re: [PATCH] comedi: integer overflow in do_insnlist_ioctl()

Ian Abbott
2011-11-23T16:15:05Z

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).

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