linux-kernel - [PATCH 10/14] random: direct all routine input via input pool

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Date:	Sat, 14 Dec 2013 21:01:44 -0500
From:	Greg Price <price@....EDU>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 10/14] random: direct all routine input via input pool

This lets us control when the nonblocking pool is reseeded from
input, even early in boot.  Our normal reseed mechanisms then
ensure that the input is used in "catastrophic reseeds",
high-entropy blobs added all at once with no possibility of output
between one part of the input and another.  If we alternate
reseed, output, reseed, output, etc., and an attacker sees the
output, then they can brute-force one reseed at a time, so that
our randomness is only slightly better than the single best reseed.

The preceding commits should ensure that until we're initialized,
we get entropy into the nonblocking pool ASAP without rate-limiting,
or sending any to the blocking pool, or losing any extra entropy
beyond our estimates, limited only by the need to batch it up into
large reseeds.  This should accomplish the important job of
getting us quickly seeded that was previously accomplished by
sending the input straight to the nonblocking pool early on.

Signed-off-by: Greg Price <price@....edu>
---
 drivers/char/random.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 58e3e81d4..ea389723f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -753,11 +753,6 @@ void add_device_randomness(const void *buf, unsigned int size)
 	_mix_pool_bytes(&input_pool, buf, size, NULL);
 	_mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
 	spin_unlock_irqrestore(&input_pool.lock, flags);
-
-	spin_lock_irqsave(&nonblocking_pool.lock, flags);
-	_mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
-	_mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
-	spin_unlock_irqrestore(&nonblocking_pool.lock, flags);
 }
 EXPORT_SYMBOL(add_device_randomness);
 
@@ -775,7 +770,6 @@ static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE;
  */
 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 {
-	struct entropy_store	*r;
 	struct {
 		long jiffies;
 		unsigned cycles;
@@ -788,8 +782,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 	sample.jiffies = jiffies;
 	sample.cycles = random_get_entropy();
 	sample.num = num;
-	r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
-	mix_pool_bytes(r, &sample, sizeof(sample), NULL);
+	mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
 
 	/*
 	 * Calculate number of bits of randomness we probably added.
@@ -823,7 +816,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 		 * Round down by 1 bit on general principles,
 		 * and limit entropy entimate to 12 bits.
 		 */
-		credit_entropy_bits(r, min_t(int, fls(delta>>1), 11));
+		credit_entropy_bits(&input_pool, min_t(int, fls(delta>>1), 11));
 	}
 	preempt_enable();
 }
@@ -848,7 +841,6 @@ static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
 
 void add_interrupt_randomness(int irq, int irq_flags)
 {
-	struct entropy_store	*r;
 	struct fast_pool	*fast_pool = &__get_cpu_var(irq_randomness);
 	struct pt_regs		*regs = get_irq_regs();
 	unsigned long		now = jiffies;
@@ -871,8 +863,9 @@ void add_interrupt_randomness(int irq, int irq_flags)
 
 	fast_pool->last = now;
 
-	r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
-	__mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
+	__mix_pool_bytes(&input_pool,
+			 &fast_pool->pool, sizeof(fast_pool->pool),
+			 NULL);
 	/*
 	 * If we don't have a valid cycle counter, and we see
 	 * back-to-back timer interrupts, then skip giving credit for
@@ -886,7 +879,7 @@ void add_interrupt_randomness(int irq, int irq_flags)
 		} else
 			fast_pool->last_timer_intr = 0;
 	}
-	credit_entropy_bits(r, 1);
+	credit_entropy_bits(&input_pool, 1);
 }
 
 #ifdef CONFIG_BLOCK
-- 
1.8.3.2

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