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Commit 43838a23 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

random: fix crng_ready() test 



The crng_init variable has three states:

0: The CRNG is not initialized at all
1: The CRNG has a small amount of entropy, hopefully good enough for
   early-boot, non-cryptographical use cases
2: The CRNG is fully initialized and we are sure it is safe for
   cryptographic use cases.

The crng_ready() function should only return true once we are in the
last state.  This addresses CVE-2018-1108.

Reported-by: default avatarJann Horn <jannh@google.com>
Fixes: e192be9d ("random: replace non-blocking pool...")
Cc: stable@kernel.org # 4.8+
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarJann Horn <jannh@google.com>
parent 5e747dd9

drivers/char/random.c

+5 −5
Original line number Diff line number Diff line
@@ -427,7 +427,7 @@ struct crng_state primary_crng = { 
 * its value (from 0->1->2).

 */

static int crng_init = 0;

#define crng_ready() (likely(crng_init > 0))

#define crng_ready() (likely(crng_init > 1))

static int crng_init_cnt = 0;

#define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)

static void _extract_crng(struct crng_state *crng,
@@ -794,7 +794,7 @@ static int crng_fast_load(const char *cp, size_t len) 


	if (!spin_trylock_irqsave(&primary_crng.lock, flags))

		return 0;

	if (crng_ready()) {

	if (crng_init != 0) {

		spin_unlock_irqrestore(&primary_crng.lock, flags);

		return 0;

	}
@@ -856,7 +856,7 @@ static void _extract_crng(struct crng_state *crng, 
{

	unsigned long v, flags;



	if (crng_init > 1 &&

	if (crng_ready() &&

	    time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL))

		crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);

	spin_lock_irqsave(&crng->lock, flags);
@@ -1139,7 +1139,7 @@ void add_interrupt_randomness(int irq, int irq_flags) 
	fast_mix(fast_pool);

	add_interrupt_bench(cycles);



	if (!crng_ready()) {

	if (unlikely(crng_init == 0)) {

		if ((fast_pool->count >= 64) &&

		    crng_fast_load((char *) fast_pool->pool,

				   sizeof(fast_pool->pool))) {
@@ -2212,7 +2212,7 @@ void add_hwgenerator_randomness(const char *buffer, size_t count, 
{

	struct entropy_store *poolp = &input_pool;



	if (!crng_ready()) {

	if (unlikely(crng_init == 0)) {

		crng_fast_load(buffer, count);

		return;

	}