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    Subject[PATCH 4.19 082/234] random: fix locking in crng_fast_load()
    Date
    From: Dominik Brodowski <linux@dominikbrodowski.net>

    commit 7c2fe2b32bf76441ff5b7a425b384e5f75aa530a upstream.

    crng_init is protected by primary_crng->lock, so keep holding that lock
    when incrementing crng_init from 0 to 1 in crng_fast_load(). The call to
    pr_notice() can wait until the lock is released; this code path cannot
    be reached twice, as crng_fast_load() aborts early if crng_init > 0.

    Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
    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 | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -647,12 +647,13 @@ static size_t crng_fast_load(const u8 *c
    p[crng_init_cnt % CHACHA20_KEY_SIZE] ^= *cp;
    cp++; crng_init_cnt++; len--; ret++;
    }
    - spin_unlock_irqrestore(&primary_crng.lock, flags);
    if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
    invalidate_batched_entropy();
    crng_init = 1;
    - pr_notice("fast init done\n");
    }
    + spin_unlock_irqrestore(&primary_crng.lock, flags);
    + if (crng_init == 1)
    + pr_notice("fast init done\n");
    return ret;
    }


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