Re: [PATCH 3/3] crypto: jitter - quit sample collection loop upon RCT failure

Stephan Mueller
2021-11-30T18:07:21Z

Am Dienstag, 30. November 2021, 15:10:09 CET schrieb Nicolai Stange:

Hi Nicolai,

> The jitterentropy collection loop in jent_gen_entropy() can in principle
> run indefinitely without making any progress if it only receives stuck
> measurements as determined by jent_stuck(). After 31 consecutive stuck
> samples, the Repetition Count Test (RCT) would fail anyway and the
> jitterentropy RNG instances moved into ->health_failure == 1 state.
> jent_gen_entropy()'s caller, jent_read_entropy() would then check for
> this ->health_failure condition and return an error if found set. It
> follows that there's absolutely no point in continuing the collection loop
> in jent_gen_entropy() once the RCT has failed.
>
> Make the jitterentropy collection loop more robust by terminating it upon
> jent_health_failure() so that it won't continue to run indefinitely without
> making any progress.
>
> Signed-off-by: Nicolai Stange <nstange@suse.de>

Reviewed-by: Stephan Mueller <smueller@chronox.de>

Thanks
Stephan

> ---
> crypto/jitterentropy.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c
> index 24e087c3f526..8f5283f28ed3 100644
> --- a/crypto/jitterentropy.c
> +++ b/crypto/jitterentropy.c
> @@ -547,7 +547,7 @@ static void jent_gen_entropy(struct rand_data *ec)
> /* priming of the ->prev_time value */
> jent_measure_jitter(ec);
>
> - while (1) {
> + while (!jent_health_failure(ec)) {
> /* If a stuck measurement is received, repeat measurement */
> if (jent_measure_jitter(ec))
> continue;

Ciao
Stephan