[Linux-kernel-mentees] Analyze syzbot report technisat_usb2_rc_query KASAN

Greg KH gregkh at linuxfoundation.org
Tue Jul 2 04:45:10 UTC 2019


On Tue, Jul 02, 2019 at 07:49:26AM +0700, Phong Tran wrote:
> Hello,
> 
> I did a checking for this report of syzbot [1]
> From the call stack of dump log:
> 
> There shows that a problem within technisat_usb2_get_ir()
> 
> BUG: KASAN: slab-out-of-bounds in technisat_usb2_get_ir
> drivers/media/usb/dvb-usb/technisat-usb2.c:664 [inline]
> BUG: KASAN: slab-out-of-bounds in technisat_usb2_rc_query+0x5fa/0x660
> drivers/media/usb/dvb-usb/technisat-usb2.c:679
> Read of size 1 at addr ffff8880a8791ea8 by task kworker/0:1/12
> 
> Take a look into while loop in technisat_usb2_get_ir().
> I recognized that a problem. The loop will not break out with the condition
> doesn't reach. Then "b++" will go wrong and buffer will be overflow.
> 
> while (1) {
> [...]
> 	b++;
> 	if (*b == 0xff) {
> 		ev.pulse = 0;
> 		ev.duration = 888888*2;
> 		ir_raw_event_store(d->rc_dev, &ev);
> 		break;
> 	}
> }
> 
> I would propose changing the loop condition by checking the address of the
> buffer. If acceptable, I will send this patch to the mailing-list.
> eg:
> 
> -       while (1) {
> +       while (b != (buf + 63)) {
> [...]
> }
> 
> Tested with syzbot, result is good [2].
> 
> [1] https://syzkaller.appspot.com/bug?extid=eaaaf38a95427be88f4b
> [2] https://groups.google.com/d/msg/syzkaller-bugs/CySBCKuUOOs/0hKq1CdjCwAJ

Great, can you submit a patch for this?

thanks,

greg k-h


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