Re: [PATCH v2 9/9] random: remove outdated INT_MAX >> 6 check in urandom_read()

Eric Biggers
2022-02-21T03:56:27Z

On Wed, Feb 09, 2022 at 02:19:19AM +0100, Jason A. Donenfeld wrote:
> In 79a8468747c5 ("random: check for increase of entropy_count because of
> signed conversion"), a number of checks were added around what values
> were passed to account(), because account() was doing fancy fixed point
> fractional arithmetic, and a user had some ability to pass large values
> directly into it. One of things in that commit was limiting those values
> to INT_MAX >> 6.
>
> However, for several years now, urandom reads no longer touch entropy
> accounting, and so this check serves no purpose. The current flow is:
>
> urandom_read_nowarn()-->get_random_bytes_user()-->chacha20_block()
>
> We arrive at urandom_read_nowarn() in the first place either via
> ordinary fops, which limits reads to MAX_RW_COUNT, or via getrandom()
> which limits reads to INT_MAX.
>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
> drivers/char/random.c | 1 -
> 1 file changed, 1 deletion(-)
>

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric