From: "Jason A. Donenfeld" Jason@zx2c4.com
commit 434537ae54ad37e93555de21b6ac8133d6d773a9 upstream.
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. The first >> 3 was for bytes to bits, and the next >> 3 was for bits to 1/8 fractional bits.
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()
Of course, we don't want that size_t to be truncated when adding it into the ssize_t. But 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 Reviewed-by: Dominik Brodowski linux@dominikbrodowski.net Reviewed-by: Jann Horn jannh@google.com Reviewed-by: Eric Biggers ebiggers@google.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/random.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1336,9 +1336,8 @@ void rand_initialize_disk(struct gendisk static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { - int ret; + ssize_t ret;
- nbytes = min_t(size_t, nbytes, INT_MAX >> 6); ret = get_random_bytes_user(buf, nbytes); trace_urandom_read(nbytes, input_pool.entropy_count); return ret;