[U-Boot] [PATCH] lib: uuid: Improve randomness of uuid values on RANDOM_UUID=y

[Lukasz Majewski]

On Fri, 26 Apr 2019 23:54:58 +0200
Eugeniu Rosca <roscaeugeniu at gmail.com> wrote:

> The random uuid values (enabled via CONFIG_RANDOM_UUID=y) on our
> platform are always the same. Below is consistent on each cold boot:
> 
>  => ### reach U-Boot prompt
>  => setenv uuid_gpt_misc
>  => gpt verify mmc 1 $partitions  
>     Verify GPT: success!
>  => print uuid_gpt_misc  
>     uuid_gpt_misc=d117f98e-6f2c-d04b-a5b2-331a19f91cb2
>  => setenv uuid_gpt_misc
>  => gpt verify mmc 1 $partitions  
>     Verify GPT: success!
>  => print uuid_gpt_misc  
>     uuid_gpt_misc=ad5ec4b6-2d9f-8544-9417-fe3bd1c9b1b3
> 
> While the uuids do change on every 'gpt {write,verify}' command,
> the values appear to be taken from the same pool, in the same order.
> 
> As a user, I expect a trully random uuid value in the above example.
> Otherwise, system/RFS designers and OS people might assume they have
> a reliable/consistent uuid passed by the bootloader, while the truth
> is U-Boot simply lacks entropy to generate a random string.
> 
> Let's use get_timer() to update the seed, same as done in commit
> da384a9d7628 ("net: rename and refactor eth_rand_ethaddr() function").
> 
> Signed-off-by: Eugeniu Rosca <erosca at de.adit-jv.com>
> ---
>  lib/uuid.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/lib/uuid.c b/lib/uuid.c
> index fa20ee39fc32..8a82cb234b88 100644
> --- a/lib/uuid.c
> +++ b/lib/uuid.c
> @@ -238,6 +238,8 @@ void gen_rand_uuid(unsigned char *uuid_bin)
>  	unsigned int *ptr = (unsigned int *)&uuid;
>  	int i;
>  
> +	srand(get_timer(0));
> +
>  	/* Set all fields randomly */
>  	for (i = 0; i < sizeof(struct uuid) / sizeof(*ptr); i++)
>  		*(ptr + i) = cpu_to_be32(rand());

Reviewed-by: Lukasz Majewski <lukma at denx.de>


Best regards,

Lukasz Majewski

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