• Jason A. Donenfeld's avatar
    random: Make crng state queryable · 9a47249d
    Jason A. Donenfeld authored
    It is very useful to be able to know whether or not get_random_bytes_wait
    / wait_for_random_bytes is going to block or not, or whether plain
    get_random_bytes is going to return good randomness or bad randomness.
    The particular use case is for mitigating certain attacks in WireGuard.
    A handshake packet arrives and is queued up. Elsewhere a worker thread
    takes items from the queue and processes them. In replying to these
    items, it needs to use some random data, and it has to be good random
    data. If we simply block until we can have good randomness, then it's
    possible for an attacker to fill the queue up with packets waiting to be
    processed. Upon realizing the queue is full, WireGuard will detect that
    it's under a denial of service attack, and behave accordingly. A better
    approach is just to drop incoming handshake packets if the crng is not
    yet initialized.
    This patch, therefore, makes that information directly accessible.
    Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
random.h 5.09 KB