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    Subject[PATCH 4.14 092/237] random: make credit_entropy_bits() always safe
    Date
    From: "Jason A. Donenfeld" <Jason@zx2c4.com>

    commit a49c010e61e1938be851f5e49ac219d49b704103 upstream.

    This is called from various hwgenerator drivers, so rather than having
    one "safe" version for userspace and one "unsafe" version for the
    kernel, just make everything safe; the checks are cheap and sensible to
    have anyway.

    Reported-by: Sultan Alsawaf <sultan@kerneltoast.com>
    Reviewed-by: Eric Biggers <ebiggers@google.com>
    Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 29 +++++++++--------------------
    1 file changed, 9 insertions(+), 20 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -447,18 +447,15 @@ static void process_random_ready_list(vo
    spin_unlock_irqrestore(&random_ready_list_lock, flags);
    }

    -/*
    - * Credit (or debit) the entropy store with n bits of entropy.
    - * Use credit_entropy_bits_safe() if the value comes from userspace
    - * or otherwise should be checked for extreme values.
    - */
    static void credit_entropy_bits(int nbits)
    {
    int entropy_count, orig;

    - if (!nbits)
    + if (nbits <= 0)
    return;

    + nbits = min(nbits, POOL_BITS);
    +
    do {
    orig = READ_ONCE(input_pool.entropy_count);
    entropy_count = min(POOL_BITS, orig + nbits);
    @@ -470,18 +467,6 @@ static void credit_entropy_bits(int nbit
    crng_reseed(&primary_crng, true);
    }

    -static int credit_entropy_bits_safe(int nbits)
    -{
    - if (nbits < 0)
    - return -EINVAL;
    -
    - /* Cap the value to avoid overflows */
    - nbits = min(nbits, POOL_BITS);
    -
    - credit_entropy_bits(nbits);
    - return 0;
    -}
    -
    /*********************************************************************
    *
    * CRNG using CHACHA20
    @@ -1525,7 +1510,10 @@ static long random_ioctl(struct file *f,
    return -EPERM;
    if (get_user(ent_count, p))
    return -EFAULT;
    - return credit_entropy_bits_safe(ent_count);
    + if (ent_count < 0)
    + return -EINVAL;
    + credit_entropy_bits(ent_count);
    + return 0;
    case RNDADDENTROPY:
    if (!capable(CAP_SYS_ADMIN))
    return -EPERM;
    @@ -1538,7 +1526,8 @@ static long random_ioctl(struct file *f,
    retval = write_pool((const char __user *)p, size);
    if (retval < 0)
    return retval;
    - return credit_entropy_bits_safe(ent_count);
    + credit_entropy_bits(ent_count);
    + return 0;
    case RNDZAPENTCNT:
    case RNDCLEARPOOL:
    /*

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