Re: [Cocci] [PATCH 1/2] Coccinelle: extend memdup_user transformation with GFP_USER

[Denis Efremov]

On 6/6/20 11:24 AM, Julia Lawall wrote:
> 
> 
> On Sat, 30 May 2020, Denis Efremov wrote:
> 
>> Match GFP_USER allocations with memdup_user.cocci rule.
>> Commit 6c2c97a24f09 ("memdup_user(): switch to GFP_USER") switched
>> memdup_user() from GFP_KERNEL to GFP_USER. In most cases it is still
>> a good idea to use memdup_user() for GFP_KERNEL allocations. The
>> motivation behind altering memdup_user() to GFP_USER is here:
>> https://lkml.org/lkml/2018/1/6/333
> 
> Should the rule somehow document the cases in which memdup_user should now
> not be used?

As for now, I can't provide a counterexample. GPF_USER is more permissive than
GFP_KERNEL. It's completely ok to use GPF_USER with copy_from_user. Given that
memdup_user() was "silently" switched to GPF_USER from GPF_KERNEL with no callside
fixes, I think it's ok to recommend to use memdup_user for GPF_KERNEL matches with
no additional restrictions.

Thanks,
Denis