Re: [PATCH] net: hso: fix null-ptr-deref during tty device unregistration

Anirudh Rayabharam
2021-04-07T18:11:54Z

On Tue, Apr 06, 2021 at 04:39:21PM -0700, David Miller wrote:
> From: Anirudh Rayabharam <mail@anirudhrb.com>
> Date: Tue, 6 Apr 2021 18:13:59 +0530
>
> > 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@syzkaller.appspotmail.com
> > Tested-by: syzbot+c49fe6089f295a05e6f8@syzkaller.appspotmail.com
> >
> > Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
>
> This adds a new build warning:
>
> CC [M] drivers/net/usb/hso.o
> drivers/net/usb/hso.c: In function ‘hso_serial_common_create’:
> drivers/net/usb/hso.c:2256:6: warning: unused variable ‘minor’ [-Wunused-variable]
>
> Please fix this and add an appropriate Fixes: tag, thank you.

I have sent out a v2 with these changes.

Thanks!

- Anirudh.