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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Alex Dewar <alex.dewar90@gmail.com>
Cc: David Howells <dhowells@redhat.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	keyrings@vger.kernel.org, linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] security: keys: Use kvfree_sensitive in a few places
Date: Fri, 11 Sep 2020 15:04:24 +0000	[thread overview]
Message-ID: <1599836664.4041.21.camel@HansenPartnership.com> (raw)
In-Reply-To: <20200911114400.82207-1-alex.dewar90@gmail.com>

On Fri, 2020-09-11 at 12:44 +0100, Alex Dewar wrote:
> In big_key.c, there are a few places where memzero_explicit + kvfree
> is used. It is better to use kvfree_sensitive instead, which is more
> readable and also prevents the compiler from eliding the call to
> memzero_explicit. Fix this.

That last bit is untrue: the compiler can't elide memzero_explicit ...
that's why it has the explicit suffix.

The original problem was a lot of people do memset(.., 0, ..); kfree()
which the compiler can elide if it understands the memory is going out
of scope.  Or the even more problematic memset(..., 0, ...) on a stack
variable before it goes out of scope.

We can argue about readability but there's no secret leak here.

James

WARNING: multiple messages have this Message-ID (diff)
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Alex Dewar <alex.dewar90@gmail.com>
Cc: David Howells <dhowells@redhat.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	keyrings@vger.kernel.org, linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] security: keys: Use kvfree_sensitive in a few places
Date: Fri, 11 Sep 2020 08:04:24 -0700	[thread overview]
Message-ID: <1599836664.4041.21.camel@HansenPartnership.com> (raw)
In-Reply-To: <20200911114400.82207-1-alex.dewar90@gmail.com>

On Fri, 2020-09-11 at 12:44 +0100, Alex Dewar wrote:
> In big_key.c, there are a few places where memzero_explicit + kvfree
> is used. It is better to use kvfree_sensitive instead, which is more
> readable and also prevents the compiler from eliding the call to
> memzero_explicit. Fix this.

That last bit is untrue: the compiler can't elide memzero_explicit ...
that's why it has the explicit suffix.

The original problem was a lot of people do memset(.., 0, ..); kfree()
which the compiler can elide if it understands the memory is going out
of scope.  Or the even more problematic memset(..., 0, ...) on a stack
variable before it goes out of scope.

We can argue about readability but there's no secret leak here.

James


  reply	other threads:[~2020-09-11 15:04 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-11 11:44 [PATCH] security: keys: Use kvfree_sensitive in a few places Alex Dewar
2020-09-11 11:44 ` Alex Dewar
2020-09-11 15:04 ` James Bottomley [this message]
2020-09-11 15:04   ` James Bottomley
2020-09-11 16:00   ` Alex Dewar
2020-09-11 16:00     ` Alex Dewar
2020-09-11 16:03     ` Alex Dewar
2020-09-11 16:03       ` Alex Dewar
2020-09-11 16:06     ` [PATCH v2] " Alex Dewar
2020-09-11 16:06       ` Alex Dewar
2020-09-11 16:05 ` [PATCH] " Denis Efremov
2020-09-11 16:05   ` Denis Efremov
2020-09-11 16:09   ` Alex Dewar
2020-09-11 16:09     ` Alex Dewar
2020-09-14 18:05   ` Jarkko Sakkinen
2020-09-14 18:05     ` Jarkko Sakkinen

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