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SubjectRe: [PATCH 4.16 163/196] random: fix crng_ready() test
On Sun, Apr 22, 2018 at 03:53:03PM +0200, Greg Kroah-Hartman wrote:
> 4.16-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> 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>

This patch has caused a regression on 4.16 using kselftest lib/printf.sh
- specifically, when it runs "/sbin/modprobe test_printf". This
regression has been detected on arm64 dragonboard 410c (not seen on
other arm64 or x86_64 devices).

/sbin/modprobe test_printf
[ 22.725551] test_printf: hashing plain 'p' has unexpected format
[ 22.726031] test_printf: failed 1 out of 236 tests
modprobe: ERROR: could not insert 'test_printf': Invalid argument

This problem has not been seen on 4.9 or 4.14 under the same
conditions.

Dan

>
> ---
> drivers/char/random.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -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,
> @@ -793,7 +793,7 @@ 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;
> }
> @@ -855,7 +855,7 @@ 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);
> @@ -1141,7 +1141,7 @@ 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))) {
> @@ -2214,7 +2214,7 @@ 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;
> }
>
>

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