Re: [PATCH] char_driver_warn_unseeded_randomness: Add null check

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jun 03, 2020 at 10:29:07PM -0400, gaurav singh wrote:
> File: drivers/char/random.c
> Function: _warn_unseeded_randomness
> 
> There is a check for previous(ptr) before dereferencing:
> 
>     if (print_once ||
>         crng_ready() ||
>         (previous && (caller == READ_ONCE(*previous))))
>         return;
> 
> However, after this, it is dereferenced without checking:
> WRITE_ONCE(*previous, caller);
> 
> To fix this, add a null check
> 
> Please find the patch below. Let me know if there's any issue.
> 
> Thanks,
> Gaurav.
> 
> 
> >From 5e53cbce018c4d57753a6740c22d826bae0aab3f Mon Sep 17 00:00:00 2001
> From: Gaurav Singh <gaurav1086@gmail.com>
> Date: Wed, 3 Jun 2020 22:23:47 -0400
> Subject: [PATCH] char_driver_warn_unseeded_randomness: Add null check for
>  previous
> 
> Signed-off-by: Gaurav Singh <gaurav1086@gmail.com>
> ---
>  drivers/char/random.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 0d10e31fd342..4f1975e7f201 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1526,7 +1526,9 @@ static void _warn_unseeded_randomness(const char
> *func_name, void *caller,
>      crng_ready() ||
>      (previous && (caller == READ_ONCE(*previous))))
>   return;
> - WRITE_ONCE(*previous, caller);
> +
> + if (previous)
> + WRITE_ONCE(*previous, caller);
>  #ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
>   print_once = true;
>  #endif
> -- 
> 2.17.1


Hi,

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