Re: [PATCH] kstrtox: make kstrtobool_from_user() very strict

[Kees Cook]

On Sat, Feb 10, 2018 at 1:11 PM, Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote:
> Once upon a time module parameter parsing code accepted
> 0, 1, y, n, Y and N for boolean values. Gratituous but contained
> to module code and thus tolerable.

And kernel command line.

> Commit ef951599074ba4fad2d0efa0a977129b41e6d203
> ("lib: move strtobool() to kstrtobool()") promoted that ugly wart
> to kstrtobool() and, more importantly, kstrtobool_from_user().
>
> Later set of accepted values was expanded to "on" and "of".
> Now there are 6+8=14(!) valid strings for a boolean.
>
> This patch reduces set of accepted values to "0" and "1"
> (with optional newline) in spirit with other kstrto*() functions.
>
> I'm starting with kstrtobool_from_user() as it is explicitly designed
> to be used for interacting with userspace. Currently there are 9 users
> all debug code, so there is hope.
>
> Please send before 4.16 so no real users start to depend on verbose behaviour.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>

Why bother? What's wrong with generous input parsing? This just
creates a divergence where none is needed.

-Kees

-- 
Kees Cook
Pixel Security