Re: [PATCH v2 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

This is a multi-part message in MIME format.On 3/10/20 1:12 PM, David Howells wrote:
> Waiman Long <longman@xxxxxxxxxx> wrote:
>
>> That is not as simple as I thought. First of that, there is not an
>> equivalent kzvfree() helper to clear the buffer first before clearing.
>> Of course, I can do that manually.
> Yeah, the actual substance of vfree() may get deferred.  It may be worth
> adding a kvzfree() that switches between kzfree() and memset(),vfree().
>
>> With patch 2, the allocated buffer length will be max(1024, keylen). The
>> security code uses kmalloc() for allocation. If we use kvalloc() here,
>> perhaps we should also use that for allocation that can be potentially
>> large like that in big_key. What do you think?
> Not for big_key: if it's larger than BIG_KEY_FILE_THRESHOLD (~1KiB) it gets
> written encrypted into shmem so that it can be swapped out to disk when not in
> use.
>
> However, other cases, sure - just be aware that on a 32-bit system,
> vmalloc/vmap space is a strictly limited resource.

Attached is an additional patch to make the transition from kmalloc() to
kvmalloc(). I put the __kvzfree() helper in internal.h for now. I plan
to send a patch later to add a kvzfree() API once there is a use case in
the kernel.

I am not going to touch other places for now to make thing simpler.

Cheers,
Longman