linux-kernel - Re: [PATCH v3 2/2] sysctl: Fix underflow value setting risk in vm

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Message-ID: <mdyg6vjy5hybv47ovw2uywlqzz4nq67bdntnpmtbaxj64pz5sz@5vx4rlsvu22a>
Date: Wed, 15 Jan 2025 11:27:12 +0100
From: Joel Granados <joel.granados@...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>, 
	Kees Cook <kees@...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 v3 2/2] sysctl: Fix underflow value setting risk in
 vm_table

On Tue, Dec 17, 2024 at 02:29:07PM +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.
Please also mention that you added a extra* arg.

> 
> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>
> ---
>  kernel/sysctl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 79e6cb1d5c48f..6d8a4fceb79aa 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2194,8 +2194,9 @@ static struct ctl_table vm_table[] = {
>  		.maxlen		= sizeof(vdso_enabled),
>  #endif
>  		.mode		= 0644,
> -		.proc_handler	= proc_dointvec,
> +		.proc_handler	= proc_dointvec_minmax,
>  		.extra1		= SYSCTL_ZERO,
> +		.extra1		= SYSCTL_ONE,
* What did you mean here?
  1. To replace extra1 with SYSCTL_ONE?
  2. To add extra2 as SYSCTL_ONE and you mistyped it as "extra1"?

* This patch conflicts with the vm_table moving out of the kernel
  directory [1] from Kaixiong Yu <yukaixiong@...wei.com> (which is also
  in sysctl-testing). I have fixed this conflict with [2], please scream
  if you see that messed up.

* Please send an updated version addressing these comments and taking
  into account that your patches will go after [1]. You can use [3] as
  your base if you prefer.

Best


[1] https://lore.kernel.org/20250111070751.2588654-14-yukaixiong@huawei.com
[2] https://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl.git/commit/?h=sysctl-testing&id=81b34e7966e84983a31c0150cbf2171605c023a3
[3] https://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl.git/commit/?h=sysctl-testing&id=2fc99f285719e0cce8df1fe21479cb9e6626c2fe

-- 

Joel Granados