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    SubjectRe: [PATCH] random: allow writes to /dev/urandom to influence fast init
    Hi!
    > > On Tue, Mar 22, 2022 at 01:14:36PM -0600, Jason A. Donenfeld wrote:
    > >> For as far back as I can tell, writing to /dev/urandom or /dev/random
    > >> will put entropy into the pool, but won't immediately use it, and won't
    > >> credit it either.
    > >
    > > Did you check kernels v4.7 and earlier? It looks like this actually changed
    > > in
    > > v4.8 when the ChaCha20 CRNG was introduced. v4.7 would mix the data written
    > > to
    > > /dev/{u,}random into {non,}blocking_pool, which would immediately be
    > > reflected
    > > in reads from /dev/{u,}random, sys_getrandom(), and get_random_bytes().
    > > Writes
    > > to /dev/{u,}random didn't affect the input_pool, which was separate.
    >
    > Oh, I suppose you might be right, actually, that v4.7 and below would
    > hash the non blocking pool, and let /dev/urandom write directly into
    > it, as something distinct from the input pool. This changed with v4.8,
    > 6 years ago, and now there are no LTS kernels that old, with most
    > small devices even having vendor kernels v4.9+. v4.8 apparently did

    We are still maintaining 4.4 for -cip project, and people running android probably still
    maintain that, too.

    > this while fixing a more extreme vulnerability of allowing unprivileged users to
    > bruteforce input bytes (in addition to allowing unbounded unprivileged lock contention).

    I assume this got fixed during the 4.4-stable series?

    Best regards,
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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