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    Subject[PATCH 5.10 043/188] net: hso: fix null-ptr-deref during tty device unregistration
    Date
    From: Anirudh Rayabharam <mail@anirudhrb.com>

    commit 8a12f8836145ffe37e9c8733dce18c22fb668b66 upstream.

    Multiple ttys try to claim the same the minor number causing a double
    unregistration of the same device. The first unregistration succeeds
    but the next one results in a null-ptr-deref.

    The get_free_serial_index() function returns an available minor number
    but doesn't assign it immediately. The assignment is done by the caller
    later. But before this assignment, calls to get_free_serial_index()
    would return the same minor number.

    Fix this by modifying get_free_serial_index to assign the minor number
    immediately after one is found to be and rename it to obtain_minor()
    to better reflect what it does. Similary, rename set_serial_by_index()
    to release_minor() and modify it to free up the minor number of the
    given hso_serial. Every obtain_minor() should have corresponding
    release_minor() call.

    Fixes: 72dc1c096c705 ("HSO: add option hso driver")
    Reported-by: syzbot+c49fe6089f295a05e6f8@syzkaller.appspotmail.com
    Tested-by: syzbot+c49fe6089f295a05e6f8@syzkaller.appspotmail.com
    Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/usb/hso.c | 33 ++++++++++++---------------------
    1 file changed, 12 insertions(+), 21 deletions(-)

    --- a/drivers/net/usb/hso.c
    +++ b/drivers/net/usb/hso.c
    @@ -611,7 +611,7 @@ static struct hso_serial *get_serial_by_
    return serial;
    }

    -static int get_free_serial_index(void)
    +static int obtain_minor(struct hso_serial *serial)
    {
    int index;
    unsigned long flags;
    @@ -619,8 +619,10 @@ static int get_free_serial_index(void)
    spin_lock_irqsave(&serial_table_lock, flags);
    for (index = 0; index < HSO_SERIAL_TTY_MINORS; index++) {
    if (serial_table[index] == NULL) {
    + serial_table[index] = serial->parent;
    + serial->minor = index;
    spin_unlock_irqrestore(&serial_table_lock, flags);
    - return index;
    + return 0;
    }
    }
    spin_unlock_irqrestore(&serial_table_lock, flags);
    @@ -629,15 +631,12 @@ static int get_free_serial_index(void)
    return -1;
    }

    -static void set_serial_by_index(unsigned index, struct hso_serial *serial)
    +static void release_minor(struct hso_serial *serial)
    {
    unsigned long flags;

    spin_lock_irqsave(&serial_table_lock, flags);
    - if (serial)
    - serial_table[index] = serial->parent;
    - else
    - serial_table[index] = NULL;
    + serial_table[serial->minor] = NULL;
    spin_unlock_irqrestore(&serial_table_lock, flags);
    }

    @@ -2230,6 +2229,7 @@ static int hso_stop_serial_device(struct
    static void hso_serial_tty_unregister(struct hso_serial *serial)
    {
    tty_unregister_device(tty_drv, serial->minor);
    + release_minor(serial);
    }

    static void hso_serial_common_free(struct hso_serial *serial)
    @@ -2253,24 +2253,22 @@ static void hso_serial_common_free(struc
    static int hso_serial_common_create(struct hso_serial *serial, int num_urbs,
    int rx_size, int tx_size)
    {
    - int minor;
    int i;

    tty_port_init(&serial->port);

    - minor = get_free_serial_index();
    - if (minor < 0)
    + if (obtain_minor(serial))
    goto exit2;

    /* register our minor number */
    serial->parent->dev = tty_port_register_device_attr(&serial->port,
    - tty_drv, minor, &serial->parent->interface->dev,
    + tty_drv, serial->minor, &serial->parent->interface->dev,
    serial->parent, hso_serial_dev_groups);
    - if (IS_ERR(serial->parent->dev))
    + if (IS_ERR(serial->parent->dev)) {
    + release_minor(serial);
    goto exit2;
    + }

    - /* fill in specific data for later use */
    - serial->minor = minor;
    serial->magic = HSO_SERIAL_MAGIC;
    spin_lock_init(&serial->serial_lock);
    serial->num_rx_urbs = num_urbs;
    @@ -2667,9 +2665,6 @@ static struct hso_device *hso_create_bul

    serial->write_data = hso_std_serial_write_data;

    - /* and record this serial */
    - set_serial_by_index(serial->minor, serial);
    -
    /* setup the proc dirs and files if needed */
    hso_log_port(hso_dev);

    @@ -2726,9 +2721,6 @@ struct hso_device *hso_create_mux_serial
    serial->shared_int->ref_count++;
    mutex_unlock(&serial->shared_int->shared_int_lock);

    - /* and record this serial */
    - set_serial_by_index(serial->minor, serial);
    -
    /* setup the proc dirs and files if needed */
    hso_log_port(hso_dev);

    @@ -3113,7 +3105,6 @@ static void hso_free_interface(struct us
    cancel_work_sync(&serial_table[i]->async_get_intf);
    hso_serial_tty_unregister(serial);
    kref_put(&serial_table[i]->ref, hso_serial_ref_free);
    - set_serial_by_index(i, NULL);
    }
    }


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