On Thu, Nov 14, 2024 at 05:25:51PM +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`
It would be interesting to know what happens when you do a
# echo (INT_MAX + 1) > /proc/sys/vm/vdso_enabled
This is the reasons why I'm interested in such a test:
1. Both proc_dointvec and proc_dointvec_minmax (calls proc_dointvec) have a
overflow check where they will return -EINVAL if what is given by the user is
greater than (unsiged long)INT_MAX; this will evaluate can evaluate to true
or false depending on the architecture where we are running.
2. I noticed that vdso_enabled is an unsigned long. And so the expectation is
that the range is 0 to ULONG_MAX, which in some cases (depending on the arch)
would not be the case.
So my question is: What is the expected range for this value? Because you might
not be getting the whole range in the cases where int is 32 bit and long is 64
bit.
>
> This patch properly sets the proc_handler to proc_dointvec_minmax.
>
> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
> ---
> kernel/sysctl.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 79e6cb1d5c48f..37b1c1a760985 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2194,7 +2194,7 @@ 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,
Any reason why extra2 is not defined. I know that it was not defined before, but
this does not mean that it will not have an upper limit. The way that I read the
situation is that this will be bounded by the overflow check done in
proc_dointvec and will have an upper limit of INT_MAX.
Please correct me if I have read the situation incorrectly.
Best
--
Joel Granados
