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Message-ID: <1587640413.23108.7.camel@suse.com>
Date: Thu, 23 Apr 2020 13:13:33 +0200
From: Oliver Neukum <oneukum@...e.com>
To: Pete Zaitcev <zaitcev@...hat.com>, Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+be5b5f86a162a6c281e6@...kaller.appspotmail.com>,
andreyknvl@...gle.com, gregkh@...uxfoundation.org,
linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in usblp_bulk_read
Am Donnerstag, den 23.04.2020, 00:10 -0500 schrieb Pete Zaitcev:
>
> I do not agree with this kind of workaround. The model we're following
> is for usb_kill_urb() to cancel the transfer. The usblp invokes it
> through usb_kill_anchored_urbs() and usblp_unlink_urbs(), as seen
> above. There can be no timer hitting anything once it returns.
Right. It seems to me that the problem is not killing an existing
transfer but a failure to check in case of new transfers whether
the device has been disconnected.
> 1104 is kzalloc for struct usblp.
>
> > > Freed by task 12266:
> > > save_stack+0x1b/0x80 mm/kasan/common.c:72
> > > set_track mm/kasan/common.c:80 [inline]
> > > kasan_set_free_info mm/kasan/common.c:337 [inline]
> > > __kasan_slab_free+0x117/0x160 mm/kasan/common.c:476
> > > slab_free_hook mm/slub.c:1444 [inline]
> > > slab_free_freelist_hook mm/slub.c:1477 [inline]
> > > slab_free mm/slub.c:3034 [inline]
> > > kfree+0xd5/0x300 mm/slub.c:3995
> > > usblp_disconnect.cold+0x24/0x29 drivers/usb/class/usblp.c:1380
> > > usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:436
> > > __device_release_driver drivers/base/dd.c:1137 [inline]
> > > device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1168
> > > bus_remove_device+0x2eb/0x5a0 drivers/base/bus.c:533
>
> 1380 is an inlined call to usblp_cleanup, which is just
> a bunch of kfree.
But that must never happen while while the device is open.
If that ever happens something is wrong with usblp->used.
> The bug report is still a bug report, but I'm pretty sure the
> culprit is the emulated HCD and/or the gadget layer. Unfortunately,
> I'm not up to speed in that subsystem. Maybe Alan can look at it?
I doubt it. Operation by a timer triggering a timeout must work.
Regards
Oliver
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