4.9-stable review patch. If anyone has any objections, please let me know.
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From: Theodore Ts'o tytso@mit.edu
commit 43838a23a05fbd13e47d750d3dfd77001536dd33 upstream.
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: Jann Horn jannh@google.com Fixes: e192be9d9a30 ("random: replace non-blocking pool...") Cc: stable@kernel.org # 4.8+ Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Jann Horn jannh@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/char/random.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
--- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -434,7 +434,7 @@ 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, @@ -800,7 +800,7 @@ static int crng_fast_load(const char *cp
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; } @@ -872,7 +872,7 @@ static void _extract_crng(struct crng_st { 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); @@ -1153,7 +1153,7 @@ void add_interrupt_randomness(int irq, i 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))) { @@ -2148,7 +2148,7 @@ void add_hwgenerator_randomness(const ch { struct entropy_store *poolp = &input_pool;
- if (!crng_ready()) { + if (unlikely(crng_init == 0)) { crng_fast_load(buffer, count); return; }