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Subject[PATCH v2] random: fix add_hwgenerator_randomness entropy accounting
Date
add_hwgenerator_randomness tries to only use the required amound of input
for fast init, but credits all the entropy if even a byte was left over.

Fix by not crediting entropy when using the input for fast init.

Signed-off-by: Jan Varho <jan.varho@gmail.com>
---
drivers/char/random.c | 23 ++++++-----------------
1 file changed, 6 insertions(+), 17 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1d8242969751..4d77de688016 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -437,11 +437,8 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
* This shouldn't be set by functions like add_device_randomness(),
* where we can't trust the buffer passed to it is guaranteed to be
* unpredictable (so it might not have any entropy at all).
- *
- * Returns the number of bytes processed from input, which is bounded
- * by CRNG_INIT_CNT_THRESH if account is true.
*/
-static size_t crng_pre_init_inject(const void *input, size_t len, bool account)
+static void crng_pre_init_inject(const void *input, size_t len, bool account)
{
static int crng_init_cnt = 0;
struct blake2s_state hash;
@@ -452,18 +449,15 @@ static size_t crng_pre_init_inject(const void *input, size_t len, bool account)
spin_lock_irqsave(&base_crng.lock, flags);
if (crng_init != 0) {
spin_unlock_irqrestore(&base_crng.lock, flags);
- return 0;
+ return;
}

- if (account)
- len = min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt);
-
blake2s_update(&hash, base_crng.key, sizeof(base_crng.key));
blake2s_update(&hash, input, len);
blake2s_final(&hash, base_crng.key);

if (account) {
- crng_init_cnt += len;
+ crng_init_cnt = min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt);
if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
++base_crng.generation;
crng_init = 1;
@@ -474,8 +468,6 @@ static size_t crng_pre_init_inject(const void *input, size_t len, bool account)

if (crng_init == 1)
pr_notice("fast init done\n");
-
- return len;
}

static void _get_random_bytes(void *buf, size_t nbytes)
@@ -1141,12 +1133,9 @@ void add_hwgenerator_randomness(const void *buffer, size_t count,
size_t entropy)
{
if (unlikely(crng_init == 0 && entropy < POOL_MIN_BITS)) {
- size_t ret = crng_pre_init_inject(buffer, count, true);
- mix_pool_bytes(buffer, ret);
- count -= ret;
- buffer += ret;
- if (!count || crng_init == 0)
- return;
+ crng_pre_init_inject(buffer, count, true);
+ mix_pool_bytes(buffer, count);
+ return;
}

/*
--
2.25.1
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