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net: hso: fix null-ptr-deref during tty device unregistration

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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: 72dc1c096c ("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>
This commit is contained in:
Anirudh Rayabharam 2021-04-07 22:57:22 +05:30 committed by David S. Miller
parent 5d1dbacde1
commit 8a12f88361
1 changed files with 12 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
drivers/net/usb/hso.c
View File

@ -611,7 +611,7 @@ static struct hso_serial *get_serial_by_index(unsigned index)
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 hso_device *hso_dev)
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(struct hso_serial *serial)
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_bulk_serial_device(
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_device(struct usb_interface *interface,
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 usb_interface *interface)
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);
}
}