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    Subject[PATCH 4.19 024/234] random: fix crash on multiple early calls to add_bootloader_randomness()
    Date
    From: Dominik Brodowski <linux@dominikbrodowski.net>

    commit f7e67b8e803185d0aabe7f29d25a35c8be724a78 upstream.

    Currently, if CONFIG_RANDOM_TRUST_BOOTLOADER is enabled, multiple calls
    to add_bootloader_randomness() are broken and can cause a NULL pointer
    dereference, as noted by Ivan T. Ivanov. This is not only a hypothetical
    problem, as qemu on arm64 may provide bootloader entropy via EFI and via
    devicetree.

    On the first call to add_hwgenerator_randomness(), crng_fast_load() is
    executed, and if the seed is long enough, crng_init will be set to 1.
    On subsequent calls to add_bootloader_randomness() and then to
    add_hwgenerator_randomness(), crng_fast_load() will be skipped. Instead,
    wait_event_interruptible() and then credit_entropy_bits() will be called.
    If the entropy count for that second seed is large enough, that proceeds
    to crng_reseed().

    However, both wait_event_interruptible() and crng_reseed() depends
    (at least in numa_crng_init()) on workqueues. Therefore, test whether
    system_wq is already initialized, which is a sufficient indicator that
    workqueue_init_early() has progressed far enough.

    If we wind up hitting the !system_wq case, we later want to do what
    would have been done there when wqs are up, so set a flag, and do that
    work later from the rand_initialize() call.

    Reported-by: Ivan T. Ivanov <iivanov@suse.de>
    Fixes: 18b915ac6b0a ("efi/random: Treat EFI_RNG_PROTOCOL output as bootloader randomness")
    Cc: stable@vger.kernel.org
    Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
    [Jason: added crng_need_done state and related logic.]
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 59 ++++++++++++++++++++++++++++++++------------------
    1 file changed, 38 insertions(+), 21 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -496,6 +496,7 @@ static struct crng_state primary_crng =
    * its value (from 0->1->2).
    */
    static int crng_init = 0;
    +static bool crng_need_final_init = false;
    #define crng_ready() (likely(crng_init > 1))
    static int crng_init_cnt = 0;
    static unsigned long crng_global_init_time = 0;
    @@ -888,6 +889,38 @@ static void crng_initialize(struct crng_
    crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
    }

    +static void crng_finalize_init(struct crng_state *crng)
    +{
    + if (crng != &primary_crng || crng_init >= 2)
    + return;
    + if (!system_wq) {
    + /* We can't call numa_crng_init until we have workqueues,
    + * so mark this for processing later. */
    + crng_need_final_init = true;
    + return;
    + }
    +
    + invalidate_batched_entropy();
    + numa_crng_init();
    + crng_init = 2;
    + process_random_ready_list();
    + wake_up_interruptible(&crng_init_wait);
    + kill_fasync(&fasync, SIGIO, POLL_IN);
    + pr_notice("crng init done\n");
    + if (unseeded_warning.missed) {
    + pr_notice("random: %d get_random_xx warning(s) missed "
    + "due to ratelimiting\n",
    + unseeded_warning.missed);
    + unseeded_warning.missed = 0;
    + }
    + if (urandom_warning.missed) {
    + pr_notice("random: %d urandom warning(s) missed "
    + "due to ratelimiting\n",
    + urandom_warning.missed);
    + urandom_warning.missed = 0;
    + }
    +}
    +
    #ifdef CONFIG_NUMA
    static void do_numa_crng_init(struct work_struct *work)
    {
    @@ -1042,26 +1075,7 @@ static void crng_reseed(struct crng_stat
    memzero_explicit(&buf, sizeof(buf));
    WRITE_ONCE(crng->init_time, jiffies);
    spin_unlock_irqrestore(&crng->lock, flags);
    - if (crng == &primary_crng && crng_init < 2) {
    - invalidate_batched_entropy();
    - numa_crng_init();
    - crng_init = 2;
    - process_random_ready_list();
    - wake_up_interruptible(&crng_init_wait);
    - pr_notice("random: crng init done\n");
    - if (unseeded_warning.missed) {
    - pr_notice("random: %d get_random_xx warning(s) missed "
    - "due to ratelimiting\n",
    - unseeded_warning.missed);
    - unseeded_warning.missed = 0;
    - }
    - if (urandom_warning.missed) {
    - pr_notice("random: %d urandom warning(s) missed "
    - "due to ratelimiting\n",
    - urandom_warning.missed);
    - urandom_warning.missed = 0;
    - }
    - }
    + crng_finalize_init(crng);
    }

    static void _extract_crng(struct crng_state *crng,
    @@ -1960,6 +1974,8 @@ int __init rand_initialize(void)
    {
    init_std_data(&input_pool);
    init_std_data(&blocking_pool);
    + if (crng_need_final_init)
    + crng_finalize_init(&primary_crng);
    crng_initialize(&primary_crng);
    crng_global_init_time = jiffies;
    if (ratelimit_disable) {
    @@ -2478,7 +2494,8 @@ void add_hwgenerator_randomness(const ch
    * We'll be woken up again once below random_write_wakeup_thresh,
    * or when the calling thread is about to terminate.
    */
    - wait_event_interruptible(random_write_wait, kthread_should_stop() ||
    + wait_event_interruptible(random_write_wait,
    + !system_wq || kthread_should_stop() ||
    ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
    mix_pool_bytes(poolp, buffer, count);
    credit_entropy_bits(poolp, entropy);

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