linux-kernel - Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree

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Message-ID: <38c5745d14cff75fe264a3bc61d19fd837baf7ad.camel@perches.com>
Date:   Wed, 17 Jun 2020 16:12:06 -0700
From:   Joe Perches <joe@...ches.com>
To:     Denis Efremov <efremov@...ras.ru>,
        Waiman Long <longman@...hat.com>,
        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>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        David Sterba <dsterba@...e.cz>,
        "Jason A . Donenfeld" <Jason@...c4.com>, linux-mm@...ck.org,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-amlogic@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-ppp@...r.kernel.org, wireguard@...ts.zx2c4.com,
        linux-wireless@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
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        linux-fscrypt@...r.kernel.org, ecryptfs@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-bluetooth@...r.kernel.org,
        linux-wpan@...r.kernel.org, linux-sctp@...r.kernel.org,
        linux-nfs@...r.kernel.org, tipc-discussion@...ts.sourceforge.net,
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Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to
 kfree_sensitive()

On Thu, 2020-06-18 at 00:31 +0300, Denis Efremov wrote:
> 
> On 6/16/20 9:53 PM, Joe Perches wrote:
> > On Mon, 2020-06-15 at 21:57 -0400, Waiman Long wrote:
> > >  v4:
> > >   - Break out the memzero_explicit() change as suggested by Dan Carpenter
> > >     so that it can be backported to stable.
> > >   - Drop the "crypto: Remove unnecessary memzero_explicit()" patch for
> > >     now as there can be a bit more discussion on what is best. It will be
> > >     introduced as a separate patch later on after this one is merged.
> > 
> > To this larger audience and last week without reply:
> > https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@perches.com/
> > 
> > Are there _any_ fastpath uses of kfree or vfree?
> > 
> > Many patches have been posted recently to fix mispairings
> > of specific types of alloc and free functions.
> 
> I've prepared a coccinelle script to highlight these mispairings in a function
> a couple of days ago: https://lkml.org/lkml/2020/6/5/953
> I've listed all the fixes in the commit message. 
> 
> Not so many mispairings actually, and most of them are harmless like:
> kmalloc(E) -> kvfree(E)
> 
> However, coccinelle script can't detect cross-functions mispairings, i.e.
> allocation in one function, free in another funtion.

Hey Denis, thanks for those patches.

If possible, it's probably better to not require these pairings
and use a single standard kfree/free function.

Given the existing ifs in kfree in slab/slob/slub, it seems
likely that adding a few more wouldn't have much impact.