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

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Message-ID: <718a9264-f1f6-4157-9e95-2e170152eb8f@clip-os.org>
Date: Wed, 15 Jan 2025 14:00:55 +0100
From: Nicolas Bouchinet <nicolas.bouchinet@...p-os.org>
To: Joel Granados <joel.granados@...nel.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

Hi Joel,

Thank's for your reply.

On 1/15/25 11:27, Joel Granados wrote:
> 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.
ACK, will push soon.
>
>> 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"?
Oh, my bad, it's indeed a mistype, extra1 should be set at SYSCTL_ZERO, 
extra2 to SYSCTL_ONE.
It seems you already corrected it in [3]. LGTM, thank's.
>
> * 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.


Thank's for the links, I'll reword the commit message on [3] since you 
already fixed the typo
and that [1] is already applied.

>
> 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
>

Best regards,

Nicolas