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

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Message-ID: <YG31yQ+SZLyl/iZJ@anirudhrb.com>
Date:   Wed, 7 Apr 2021 23:41:21 +0530
From:   Anirudh Rayabharam <mail@...rudhrb.com>
To:     David Miller <davem@...emloft.net>
Cc:     kuba@...nel.org, oneukum@...e.com, kernel@...il.dk,
        geert@...ux-m68k.org, zhengyongjun3@...wei.com, rkovhaev@...il.com,
        gregkh@...uxfoundation.org,
        syzbot+c49fe6089f295a05e6f8@...kaller.appspotmail.com,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: hso: fix null-ptr-deref during tty device
 unregistration

On Tue, Apr 06, 2021 at 04:39:21PM -0700, David Miller wrote:
> From: Anirudh Rayabharam <mail@...rudhrb.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@...kaller.appspotmail.com
> > Tested-by: syzbot+c49fe6089f295a05e6f8@...kaller.appspotmail.com
> > 
> > Signed-off-by: Anirudh Rayabharam <mail@...rudhrb.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.