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    Subject[PATCH 4.9 043/264] random: fix soft lockup when trying to read from an uninitialized blocking pool
    Date
    From: Theodore Ts'o <tytso@mit.edu>

    commit 58be0106c5306b939b07b4b8bf00669a20593f4b upstream.

    Fixes: eb9d1bf079bb: "random: only read from /dev/random after its pool has received 128 bits"
    Reported-by: kernel test robot <lkp@intel.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 16 +++++++++++++---
    1 file changed, 13 insertions(+), 3 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -774,8 +774,11 @@ retry:
    if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
    goto retry;

    - if (has_initialized)
    + if (has_initialized) {
    r->initialized = 1;
    + wake_up_interruptible(&random_read_wait);
    + kill_fasync(&fasync, SIGIO, POLL_IN);
    + }

    trace_credit_entropy_bits(r->name, nbits,
    entropy_count >> ENTROPY_SHIFT, _RET_IP_);
    @@ -791,6 +794,13 @@ retry:
    entropy_bits = r->entropy_count >> ENTROPY_SHIFT;
    }

    + /* initialize the blocking pool if necessary */
    + if (entropy_bits >= random_read_wakeup_bits &&
    + !other->initialized) {
    + schedule_work(&other->push_work);
    + return;
    + }
    +
    /* should we wake readers? */
    if (entropy_bits >= random_read_wakeup_bits &&
    wq_has_sleeper(&random_read_wait)) {
    @@ -1992,8 +2002,8 @@ _random_read(int nonblock, char __user *
    return -EAGAIN;

    wait_event_interruptible(random_read_wait,
    - ENTROPY_BITS(&input_pool) >=
    - random_read_wakeup_bits);
    + blocking_pool.initialized &&
    + (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits));
    if (signal_pending(current))
    return -ERESTARTSYS;
    }

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