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Commit 7e07beda authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Greg Kroah-Hartman
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random: fix crash on multiple early calls to add_bootloader_randomness() 



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: default avatarIvan T. Ivanov <iivanov@suse.de>
Fixes: 18b915ac ("efi/random: Treat EFI_RNG_PROTOCOL output as bootloader randomness")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
[Jason: added crng_need_done state and related logic.]
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 517ab153

drivers/char/random.c

+38 −21
Original line number Diff line number Diff line
@@ -497,6 +497,7 @@ 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;
@@ -889,6 +890,38 @@ static void crng_initialize(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("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)

{
@@ -1044,26 +1077,7 @@ 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);

		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,
@@ -1962,6 +1976,8 @@ 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) {
@@ -2493,7 +2509,8 @@ 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);