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Re: [libvirt] [PATCH 1/2] util: Don't overflow in virRandomBits



On Wed, Aug 01, 2018 at 01:44:32PM +0200, Michal Privoznik wrote:
> The function is supposed to return up to 64bit long integer. In
> order to do that it calls virRandomBytes() to fill the integer
> with random bytes and then masks out everything but requested
> bits. However, when doing that it shifts 1U and not 1ULL. So
> effectively, requesting 32 random bis or more always return 0
> which is not random enough.
> 
> Signed-off-by: Michal Privoznik <mprivozn redhat com>
> ---
>  src/util/virrandom.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/util/virrandom.c b/src/util/virrandom.c
> index 01cc82a052..3c011a8615 100644
> --- a/src/util/virrandom.c
> +++ b/src/util/virrandom.c
> @@ -68,7 +68,7 @@ uint64_t virRandomBits(int nbits)
>          return 0;
>      }
>  
> -    ret &= (1U << nbits) - 1;
> +    ret &= (1ULL << nbits) - 1;
>      return ret;
>  }

Reviewed-by: Daniel P. Berrangé <berrange redhat com>

Regards,
Daniel
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