From c1fc9536d031aa4fe7a39f6e2cecea0476fabe2a Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 9 Feb 2022 18:42:13 +0100 Subject: [PATCH] random: zero buffer after reading entropy from userspace 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 Reviewed-by: Jann Horn Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 0160d36b9dda..f9187a2dae48 100644 --- 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 file *file, poll_table *wait) 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,