[PATCH] random: use urandom instead of random for now and speed up crng init

[Sultan Alsawaf]

With the fixes for CVE-2018-1108, /dev/random now requires user-provided
entropy on quite a few machines lacking high levels of boot entropy
in order to complete its initialization. This causes issues on environments
where userspace depends on /dev/random in order to finish booting
completely (i.e., userspace will remain stuck, unable to boot, waiting for
entropy more-or-less indefinitely until the user provides it via something
like keystrokes or mouse movements).

As a temporary workaround, redirect /dev/random to /dev/urandom instead,
and speed up the initialization process by slightly relaxing the
threshold for interrupts to go towards adding one bit of entropy credit
(only until initialization is complete).

Signed-off-by: Sultan Alsawaf <sultanxda@xxxxxxxxx>
---
 drivers/char/mem.c    | 3 ++-
 drivers/char/random.c | 9 ++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index ffeb60d3434c..cc9507f01c79 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -870,7 +870,8 @@ static const struct memdev {
 #endif
 	 [5] = { "zero", 0666, &zero_fops, 0 },
 	 [7] = { "full", 0666, &full_fops, 0 },
-	 [8] = { "random", 0666, &random_fops, 0 },
+	 /* Redirect /dev/random to /dev/urandom until /dev/random is fixed */
+	 [8] = { "random", 0666, &urandom_fops, 0 },
 	 [9] = { "urandom", 0666, &urandom_fops, 0 },
 #ifdef CONFIG_PRINTK
 	[11] = { "kmsg", 0644, &kmsg_fops, 0 },
diff --git a/drivers/char/random.c b/drivers/char/random.c
index d9e38523b383..bce3b43cdd3b 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1200,9 +1200,12 @@ void add_interrupt_randomness(int irq)
 		return;
 	}
 
-	if ((fast_pool->count < 64) &&
-	    !time_after(now, fast_pool->last + HZ))
-		return;
+	if (fast_pool->count < 64) {
+		unsigned long timeout = crng_ready() ? HZ : HZ / 4;
+
+		if (!time_after(now, fast_pool->last + timeout))
+			return;
+	}
 
 	r = &input_pool;
 	if (!spin_trylock(&r->lock))
-- 
2.14.1