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    Subject[PATCH 5.10 099/163] random: cleanup UUID handling
    Date
    From: "Jason A. Donenfeld" <Jason@zx2c4.com>

    commit 64276a9939ff414f2f0db38036cf4e1a0a703394 upstream.

    Rather than hard coding various lengths, we can use the right constants.
    Strings should be `char *` while buffers should be `u8 *`. Rather than
    have a nonsensical and unused maxlength, just remove it. Finally, use
    snprintf instead of sprintf, just out of good hygiene.

    As well, remove the old comment about returning a binary UUID via the
    binary sysctl syscall. That syscall was removed from the kernel in 5.5,
    and actually, the "uuid_strategy" function and related infrastructure
    for even serving it via the binary sysctl syscall was removed with
    894d2491153a ("sysctl drivers: Remove dead binary sysctl support") back
    in 2.6.33.

    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, 13 insertions(+), 16 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -1661,22 +1661,25 @@ const struct file_operations urandom_fop
    static int sysctl_random_min_urandom_seed = 60;
    static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS;
    static int sysctl_poolsize = POOL_BITS;
    -static char sysctl_bootid[16];
    +static u8 sysctl_bootid[UUID_SIZE];

    /*
    * This function is used to return both the bootid UUID, and random
    - * UUID. The difference is in whether table->data is NULL; if it is,
    + * UUID. The difference is in whether table->data is NULL; if it is,
    * then a new UUID is generated and returned to the user.
    - *
    - * If the user accesses this via the proc interface, the UUID will be
    - * returned as an ASCII string in the standard UUID format; if via the
    - * sysctl system call, as 16 bytes of binary data.
    */
    static int proc_do_uuid(struct ctl_table *table, int write, void *buffer,
    size_t *lenp, loff_t *ppos)
    {
    - struct ctl_table fake_table;
    - unsigned char buf[64], tmp_uuid[16], *uuid;
    + u8 tmp_uuid[UUID_SIZE], *uuid;
    + char uuid_string[UUID_STRING_LEN + 1];
    + struct ctl_table fake_table = {
    + .data = uuid_string,
    + .maxlen = UUID_STRING_LEN
    + };
    +
    + if (write)
    + return -EPERM;

    uuid = table->data;
    if (!uuid) {
    @@ -1691,12 +1694,8 @@ static int proc_do_uuid(struct ctl_table
    spin_unlock(&bootid_spinlock);
    }

    - sprintf(buf, "%pU", uuid);
    -
    - fake_table.data = buf;
    - fake_table.maxlen = sizeof(buf);
    -
    - return proc_dostring(&fake_table, write, buffer, lenp, ppos);
    + snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
    + return proc_dostring(&fake_table, 0, buffer, lenp, ppos);
    }

    extern struct ctl_table random_table[];
    @@ -1732,13 +1731,11 @@ struct ctl_table random_table[] = {
    {
    .procname = "boot_id",
    .data = &sysctl_bootid,
    - .maxlen = 16,
    .mode = 0444,
    .proc_handler = proc_do_uuid,
    },
    {
    .procname = "uuid",
    - .maxlen = 16,
    .mode = 0444,
    .proc_handler = proc_do_uuid,
    },

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