Re: [PATCH v2 1/3] kasan: move checks to do_strncpy_from_user

[Andrey Konovalov]

On Sun, Oct 13, 2024 at 3:01 PM Sabyrzhan Tasbolatov
<snovitoll@xxxxxxxxx> wrote:
>
> Since in the commit 2865baf54077("x86: support user address masking instead
> of non-speculative conditional") do_strncpy_from_user() is called from
> multiple places, we should sanitize the kernel *dst memory and size
> which were done in strncpy_from_user() previously.
>
> Fixes: 2865baf54077 ("x86: support user address masking instead of non-speculative conditional")
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx>
> ---
>  lib/strncpy_from_user.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
> index 989a12a6787..f36ad821176 100644
> --- a/lib/strncpy_from_user.c
> +++ b/lib/strncpy_from_user.c
> @@ -31,6 +31,9 @@ static __always_inline long do_strncpy_from_user(char *dst, const char __user *s
>         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
>         unsigned long res = 0;
>
> +       kasan_check_write(dst, count);
> +       check_object_size(dst, count, false);
> +
>         if (IS_UNALIGNED(src, dst))
>                 goto byte_at_a_time;
>
> @@ -142,8 +145,6 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
>                 if (max > count)
>                         max = count;
>
> -               kasan_check_write(dst, count);
> -               check_object_size(dst, count, false);
>                 if (user_read_access_begin(src, max)) {
>                         retval = do_strncpy_from_user(dst, src, count, max);
>                         user_read_access_end();
> --
> 2.34.1
>

Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>