On Tue, Apr 06, 2021 at 06:13:59PM +0530, Anirudh Rayabharam wrote: > 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. > > Reported-by: syzbot+c49fe6089f295a05e6f8@xxxxxxxxxxxxxxxxxxxxxxxxx > Tested-by: syzbot+c49fe6089f295a05e6f8@xxxxxxxxxxxxxxxxxxxxxxxxx > > Signed-off-by: Anirudh Rayabharam <mail@xxxxxxxxxxxxx> > --- > drivers/net/usb/hso.c | 32 ++++++++++++-------------------- > 1 file changed, 12 insertions(+), 20 deletions(-) > > diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c > index 31d51346786a..295ca330e70c 100644 > --- a/drivers/net/usb/hso.c > +++ b/drivers/net/usb/hso.c > @@ -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; Minor note, you might want to convert this to use an idr structure in the future, this "loop and find a free minor" isn't really needed now that we have a data structure that does this all for us :) But that's not going to fix this issue, that's for future changes. thanks, greg k-h