linux-kernel - Re: [PATCH 1/2] mm, treewide: Rename kzfree() to kfree

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Date:   Wed, 15 Apr 2020 01:01:06 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
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Subject: Re: [PATCH 1/2] mm, treewide: Rename kzfree() to kfree_sensitive()

On Mon, Apr 13, 2020 at 05:15:49PM -0400, Waiman Long wrote:
> As said by Linus:
> 
>   A symmetric naming is only helpful if it implies symmetries in use.
>   Otherwise it's actively misleading.

As the btrfs example proves - people can be tempted by this false
symmetry to pair kzalloc with kzfree, which isn't what we wanted.

>   In "kzalloc()", the z is meaningful and an important part of what the
>   caller wants.
> 
>   In "kzfree()", the z is actively detrimental, because maybe in the
>   future we really _might_ want to use that "memfill(0xdeadbeef)" or
>   something. The "zero" part of the interface isn't even _relevant_.
> 
> The main reason that kzfree() exists is to clear sensitive information
> that should not be leaked to other future users of the same memory
> objects.
> 
> Rename kzfree() to kfree_sensitive() to follow the example of the
> recently added kvfree_sensitive() and make the intention of the API
> more explicit. In addition, memzero_explicit() is used to clear the
> memory to make sure that it won't get optimized away by the compiler.
> 
> The renaming is done by using the command sequence:
> 
>   git grep -w --name-only kzfree |\
>   xargs sed -i 's/\bkzfree\b/kfree_sensitive/'
> 
> followed by some editing of the kfree_sensitive() kerneldoc and the
> use of memzero_explicit() instead of memset().
> 
> Suggested-by: Joe Perches <joe@...ches.com>
> Signed-off-by: Waiman Long <longman@...hat.com>

Looks good to me. Thanks for fixing this very old mistake.

Acked-by: Johannes Weiner <hannes@...xchg.org>