Re: [PATCH] sysctl: Check name array length in deprecated_sysctl_warning()

[Kees Cook]

On Wed, May 24, 2017 at 5:21 AM, Mateusz Jurczyk <mjurczyk@xxxxxxxxxx> wrote:
> Prevent use of uninitialized memory (originating from the stack frame of
> do_sysctl()) by verifying that the name array is filled with sufficient
> input data before comparing its specific entries with integer constants.
>
> Through timing measurement or analyzing the kernel debug logs, a user-mode
> program could potentially infer the results of comparisons against the
> uninitialized memory, and acquire some (very limited) information about the
> state of the kernel stack. The change also eliminates possible future
> warnings by tools such as KMSAN and other code checkers /
> instrumentations.
>
> Signed-off-by: Mateusz Jurczyk <mjurczyk@xxxxxxxxxx>

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  kernel/sysctl_binary.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
> index ece4b177052b..38d6ba22a209 100644
> --- a/kernel/sysctl_binary.c
> +++ b/kernel/sysctl_binary.c
> @@ -1346,7 +1346,7 @@ static void deprecated_sysctl_warning(const int *name, int nlen)
>          * CTL_KERN/KERN_VERSION is used by older glibc and cannot
>          * ever go away.
>          */
> -       if (name[0] == CTL_KERN && name[1] == KERN_VERSION)
> +       if (nlen >= 2 && name[0] == CTL_KERN && name[1] == KERN_VERSION)
>                 return;
>
>         if (printk_ratelimit()) {
> --
> 2.13.0.219.gdb65acc882-goog
>



-- 
Kees Cook
Pixel Security