RE: [PATCH v4 2/6] treewide: use prandom_u32_max() when possible

David Laight
2022-10-08T22:09:29Z

From: Jason A. Donenfeld
> Sent: 07 October 2022 19:01
>
> Rather than incurring a division or requesting too many random bytes for
> the given range, use the prandom_u32_max() function, which only takes
> the minimum required bytes from the RNG and avoids divisions.
>
...
> --- a/lib/cmdline_kunit.c
> +++ b/lib/cmdline_kunit.c
> @@ -76,7 +76,7 @@ static void cmdline_test_lead_int(struct kunit *test)
> int rc = cmdline_test_values[i];
> int offset;
>
> - sprintf(in, "%u%s", prandom_u32_max(256), str);
> + sprintf(in, "%u%s", get_random_int() % 256, str);
> /* Only first '-' after the number will advance the pointer */
> offset = strlen(in) - strlen(str) + !!(rc == 2);
> cmdline_do_one_test(test, in, rc, offset);
> @@ -94,7 +94,7 @@ static void cmdline_test_tail_int(struct kunit *test)
> int rc = strcmp(str, "") ? (strcmp(str, "-") ? 0 : 1) : 1;
> int offset;
>
> - sprintf(in, "%s%u", str, prandom_u32_max(256));
> + sprintf(in, "%s%u", str, get_random_int() % 256);
> /*
> * Only first and leading '-' not followed by integer
> * will advance the pointer.

Something has gone backwards here....
And get_random_u8() looks a better fit.

David

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