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 --- drivers/char/random.c | 56 +++++++++++++++++++++++++++---------------- 1 file changed, 36 insertions(+), 20 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c index 82db125aaed7..144e8841bff4 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -468,6 +468,7 @@ 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; @@ -835,6 +836,36 @@ static void __init crng_initialize_primary(struct crng_state *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("%d get_random_xx warning(s) missed due to ratelimiting\n", + unseeded_warning.missed); + unseeded_warning.missed = 0; + } + if (urandom_warning.missed) { + pr_notice("%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) { @@ -989,25 +1020,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r) 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); - kill_fasync(&fasync, SIGIO, POLL_IN); - pr_notice("crng init done\n"); - if (unseeded_warning.missed) { - pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n", - unseeded_warning.missed); - unseeded_warning.missed = 0; - } - if (urandom_warning.missed) { - pr_notice("%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, @@ -1780,6 +1793,8 @@ static void __init init_std_data(struct entropy_store *r) int __init rand_initialize(void) { init_std_data(&input_pool); + if (crng_need_final_init) + crng_finalize_init(&primary_crng); crng_initialize_primary(&primary_crng); crng_global_init_time = jiffies; if (ratelimit_disable) { @@ -2288,7 +2303,8 @@ void add_hwgenerator_randomness(const char *buffer, size_t count, * 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);