[PATCH 4.9 125/264] random: zero buffer after reading entropy from userspace

Greg Kroah-Hartman
2022-06-23T16:55:18Z

From: "Jason A. Donenfeld" <Jason@zx2c4.com>

commit 7b5164fb1279bf0251371848e40bae646b59b3a8 upstream.

This buffer may contain entropic data that shouldn't stick around longer
than needed, so zero out the temporary buffer at the end of write_pool().

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -552,6 +552,7 @@ static void crng_reseed(void)
int entropy_count;
unsigned long next_gen;
u8 key[CHACHA20_KEY_SIZE];
+ bool finalize_init = false;

/*
* First we make sure we have POOL_MIN_BITS of entropy in the pool,
@@ -579,12 +580,14 @@ static void crng_reseed(void)
++next_gen;
WRITE_ONCE(base_crng.generation, next_gen);
WRITE_ONCE(base_crng.birth, jiffies);
- spin_unlock_irqrestore(&base_crng.lock, flags);
- memzero_explicit(key, sizeof(key));
-
if (crng_init < 2) {
invalidate_batched_entropy();
crng_init = 2;
+ finalize_init = true;
+ }
+ spin_unlock_irqrestore(&base_crng.lock, flags);
+ memzero_explicit(key, sizeof(key));
+ if (finalize_init) {
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
@@ -1386,19 +1389,24 @@ static unsigned int random_poll(struct f
static int write_pool(const char __user *ubuf, size_t count)
{
size_t len;
+ int ret = 0;
u8 block[BLAKE2S_BLOCK_SIZE];

while (count) {
len = min(count, sizeof(block));
- if (copy_from_user(block, ubuf, len))
- return -EFAULT;
+ if (copy_from_user(block, ubuf, len)) {
+ ret = -EFAULT;
+ goto out;
+ }
count -= len;
ubuf += len;
mix_pool_bytes(block, len);
cond_resched();
}

- return 0;
+out:
+ memzero_explicit(block, sizeof(block));
+ return ret;
}

static ssize_t random_write(struct file *file, const char __user *buffer,