linux-kernel - Re: [PATCH v4 2/2] sysctl: Fix underflow value setting risk in vm

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Message-ID: <202501151632.9FF3FF0@keescook>
Date: Wed, 15 Jan 2025 16:32:33 -0800
From: Kees Cook <kees@...nel.org>
To: nicolas.bouchinet@...p-os.org
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Joel Granados <j.granados@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Horman <nhorman@...driver.com>, Lin Feng <linf@...gsu.com>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v4 2/2] sysctl: Fix underflow value setting risk in
 vm_table

On Wed, Jan 15, 2025 at 02:22:09PM +0100, nicolas.bouchinet@...p-os.org wrote:
> From: Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>
> 
> Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
> fixes underflow value setting risk in vm_table but misses vdso_enabled
> sysctl.
> 
> vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
> avoid negative value writes but the proc_handler is proc_dointvec and
> not proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
> 
> The following command thus works :
> 
> `# echo -1 > /proc/sys/vm/vdso_enabled`
> 
> This patch properly sets the proc_handler to proc_dointvec_minmax.
> In addition to .extra1, .extra2 is set to SYSCTL_ONE. The sysctl is
> thus bounded between 0 and 1.
> 
> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook