random: Do not ignore early device randomness

PATCH Applied Kees Cook 1 participant 1 message Jun 26, 2017 Random number driver

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Kees Cook

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2017-06-26 23:30 UTC #0 lore raw

PATCH 1/1 random: Do not ignore early device randomness

The add_device_randomness() function would ignore incoming bytes if the crng wasn't ready. This additionally makes sure to make an early enough call to add_latent_entropy() to influence the initial stack canary, which is especially important on non-x86 systems where it stays the same through the life of the boot.

Signed-off-by Kees Cook <[email protected]>

---
 drivers/char/random.c | 5 +++++
 init/main.c           | 1 +
 2 files changed, 6 insertions(+)

drivers/char/random.c +5 -0

index 01a260f67437..23cab7a8c1c1 100644
@@ -987,6 +987,11 @@ void add_device_randomness(const void *buf, unsigned int size)
 	unsigned long time = random_get_entropy() ^ jiffies;
 	unsigned long flags;
 
+	if (!crng_ready()) {
+		crng_fast_load(buf, size);
+		return;
+	}
+
 	trace_add_device_randomness(size, _RET_IP_);
 	spin_lock_irqsave(&input_pool.lock, flags);
 	_mix_pool_bytes(&input_pool, buf, size);

init/main.c +1 -0

index f866510472d7..6b2c3ab7d76b 100644
@@ -497,6 +497,7 @@ asmlinkage __visible void __init start_kernel(void)
 	/*
 	 * Set up the initial canary ASAP:
 	 */
+	add_latent_entropy();
 	boot_init_stack_canary();
 
 	cgroup_init_early();

Signature · 6 lines

2.7.4


-- 
Kees Cook
Pixel Security