Re: KASAN: use-after-free Read in dvb_usb_device_exit

[Hans Verkuil <hverkuil@xs4all.nl>]

On 4/15/19 1:12 PM, Oliver Neukum wrote:
> On Fr, 2019-04-12 at 04:46 -0700, syzbot wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    9a33b369 usb-fuzzer: main usb gadget fuzzer driver
>> git tree:       https://github.com/google/kasan/tree/usb-fuzzer
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1643974b200000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=23e37f59d94ddd15
>> dashboard link: https://syzkaller.appspot.com/bug?extid=26ec41e9f788b3eba396
>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12f5efa7200000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1395a0f3200000
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+26ec41e9f788b3eba396@syzkaller.appspotmail.com
>>
>> dvb-usb: schedule remote query interval to 150 msecs.
>> dw2102: su3000_power_ctrl: 0, initialized 1
>> dvb-usb: TeVii S421 PCI successfully initialized and connected.
>> usb 1-1: USB disconnect, device number 2
> 
> Hi,
> 
> proposed fix. If nobody objects, I will submit it.
> 
> 	Regards
> 		Oliver
> 
> From d6097d205ac61745334b79639d3b8b910ae66c71 Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oneukum@suse.com>
> Date: Mon, 15 Apr 2019 13:06:01 +0200
> Subject: [PATCH] dvb: usb: fix use after free in dvb_usb_device_exit
> 
> dvb_usb_device_exit() frees and uses teh device name in that order
> Fix by storing the name in a buffer before freeing it
> 
> Signed-off-by: Oliver Neukum <oneukum@suse.com>
> Reported-by: syzbot+26ec41e9f788b3eba396@syzkaller.appspotmail.com
> ---
>  drivers/media/usb/dvb-usb/dvb-usb-init.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> index 99951e02a880..2e1670cc3903 100644
> --- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
> +++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> @@ -288,13 +288,18 @@ void dvb_usb_device_exit(struct usb_interface *intf)
>  {
>  	struct dvb_usb_device *d = usb_get_intfdata(intf);
>  	const char *name = "generic DVB-USB module";
> +	char identifier[40];
>  
>  	usb_set_intfdata(intf, NULL);
>  	if (d != NULL && d->desc != NULL) {
>  		name = d->desc->name;
> +		memcpy(identifier, name, 39);
> +		identifier[39] = NULL;
>  		dvb_usb_exit(d);

Why not just move this to after the info()? You'll need to repeat the
'if' in that case, but that way there is no need to memcpy anything.

Regards,

	Hans

> +	} else {
> +		memcpy(identifier, name, 39);
>  	}
> -	info("%s successfully deinitialized and disconnected.", name);
> +	info("%s successfully deinitialized and disconnected.", identifier);
>  
>  }
>  EXPORT_SYMBOL(dvb_usb_device_exit);
>