Re: [PATCH] arm: sys_oabi-compat: Use kmalloc_array() in two functions

SF Markus Elfring
2016-08-26T13:22:29Z

>> Multiplications for the size determination of memory allocations
>> indicated that array data structures should be processed.
>
> I'm afraid the above comment doesn't mean much to me, can you rephrase?

Yes, of course.

How verbose should the explanation for this update suggestion become?

> Maybe:
>
> "Multiplications for kmalloc size arguments are liable to overflow,
> potentially causing a potential security issue. Using kmalloc_array()
> allows the overflow to be caught and the allocation failed. Switch
> these callsites to kmalloc_array()."

Thanks for your wording variant.

>> @@ -285,7 +285,7 @@ asmlinkage long sys_oabi_epoll_wait(int epfd,
>> return -EINVAL;
>> if (!access_ok(VERIFY_WRITE, events, sizeof(*events) * maxevents))
>> return -EFAULT;
>> - kbuf = kmalloc(sizeof(*kbuf) * maxevents, GFP_KERNEL);
>> + kbuf = kmalloc_array(maxevents, sizeof(*kbuf), GFP_KERNEL);
>
> kmalloc_array() here actually buys us no additional safety at either
> of the callsites in your patch

Can this inline function apply a few sanity checks in a consistent way?
http://lxr.free-electrons.com/source/include/linux/slab.h#L564

> - we need to have carefully checked the values to ensure
> they don't overflow prior to the kmalloc for other reasons.

Are there any more constraints to consider?

> That's probably something that should be noted in the commit message too,
> so reviewers have the confidence that you're not blindly changing everything...

I imagine that a few contributors can get mixed feelings from a bunch
of my recent patches. There is a significant patch number in the works
for various Linux software modules.

Regards,
Markus