Re: [PATCH v4 2/2] sysctl: Fix underflow value setting risk in vm_table

[Kees Cook]

On Wed, Jan 15, 2025 at 02:22:09PM +0100, nicolas.bouchinet@xxxxxxxxxxx wrote:
> From: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
> 
> 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@xxxxxxxxxxx>

Reviewed-by: Kees Cook <kees@xxxxxxxxxx>

-- 
Kees Cook