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    Subject[PATCH 4.19 090/234] random: zero buffer after reading entropy from userspace
    Date
    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
    @@ -500,6 +500,7 @@ 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,
    @@ -527,12 +528,14 @@ 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);
    @@ -1334,19 +1337,24 @@ static __poll_t random_poll(struct file
    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,

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