netdev - Re: [PATCH v4 1/3] mm/slab: Use memzero

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Date:   Tue, 16 Jun 2020 12:08:07 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Waiman Long <longman@...hat.com>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        linux-btrfs@...r.kernel.org,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        David Sterba <dsterba@...e.cz>,
        David Howells <dhowells@...hat.com>, linux-mm@...ck.org,
        linux-sctp@...r.kernel.org, keyrings@...r.kernel.org,
        kasan-dev@...glegroups.com,
        linux-stm32@...md-mailman.stormreply.com,
        devel@...verdev.osuosl.org, linux-cifs@...r.kernel.org,
        linux-scsi@...r.kernel.org, James Morris <jmorris@...ei.org>,
        Matthew Wilcox <willy@...radead.org>,
        linux-wpan@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
        linux-pm@...r.kernel.org, ecryptfs@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        virtualization@...ts.linux-foundation.org,
        linux-integrity@...r.kernel.org, linux-nfs@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
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        stable@...r.kernel.org, linux-bluetooth@...r.kernel.org,
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        linux-crypto@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        wireguard@...ts.zx2c4.com, linux-ppp@...r.kernel.org
Subject: Re: [PATCH v4 1/3] mm/slab: Use memzero_explicit() in kzfree()

On Tue, Jun 16, 2020 at 08:42:08AM +0200, Michal Hocko wrote:
> On Mon 15-06-20 21:57:16, Waiman Long wrote:
> > The kzfree() function is normally used to clear some sensitive
> > information, like encryption keys, in the buffer before freeing it back
> > to the pool. Memset() is currently used for the buffer clearing. However,
> > it is entirely possible that the compiler may choose to optimize away the
> > memory clearing especially if LTO is being used. To make sure that this
> > optimization will not happen, memzero_explicit(), which is introduced
> > in v3.18, is now used in kzfree() to do the clearing.
> > 
> > Fixes: 3ef0e5ba4673 ("slab: introduce kzfree()")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Waiman Long <longman@...hat.com>
> 
> Acked-by: Michal Hocko <mhocko@...e.com>
> 
> Although I am not really sure this is a stable material. Is there any
> known instance where the memset was optimized out from kzfree?

I told him to add the stable.  Otherwise it will just get reported to
me again.  It's a just safer to backport it before we forget.

regards,
dan carpenter