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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 5 May 2020 15:44:58 +0200
Message-ID: <CACT4Y+YqeYnH7ZynaAOhddCQF=yoV-=2QSV+doAA0sW6Nxe71w@mail.gmail.com>
Subject: Re: KASAN: slab-out-of-bounds Write in betop_probe
To:     Oliver Neukum <oneukum@suse.com>
Cc:     syzbot <syzbot+07efed3bc5a1407bd742@syzkaller.appspotmail.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        "open list:HID CORE LAYER" <linux-input@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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,On Tue, May 5, 2020 at 3:23 PM Oliver Neukum <oneukum@suse.com> wrote:
>
> Am Montag, den 10.02.2020, 17:16 -0800 schrieb syzbot:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    e5cd56e9 usb: gadget: add raw-gadget interface
> > git tree:       https://github.com/google/kasan.git usb-fuzzer
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1517fed9e00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=8cff427cc8996115
> > dashboard link: https://syzkaller.appspot.com/bug?extid=07efed3bc5a1407bd742
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=147026b5e00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1683b6b5e00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+07efed3bc5a1407bd742@syzkaller.appspotmail.com
> >
> > betop 0003:20BC:5500.0001: unknown main item tag 0x0
> > betop 0003:20BC:5500.0001: hidraw0: USB HID v0.00 Device [HID 20bc:5500] on usb-dummy_hcd.0-1/input0
> > ==================================================================
> > BUG: KASAN: slab-out-of-bounds in set_bit include/asm-generic/bitops/instrumented-atomic.h:28 [inline]
> > BUG: KASAN: slab-out-of-bounds in betopff_init drivers/hid/hid-betopff.c:99 [inline]
> > BUG: KASAN: slab-out-of-bounds in betop_probe+0x396/0x570 drivers/hid/hid-betopff.c:134
> > Write of size 8 at addr ffff8881d4f43ac0 by task kworker/1:2/94
> >
> > Freed by task 12:
> >  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:3024 [inline]
> >  kfree+0xd5/0x300 mm/slub.c:3976
> >  urb_destroy drivers/usb/core/urb.c:26 [inline]
> >  kref_put include/linux/kref.h:65 [inline]
> >
>
> Hi,
>
> this indicates that I am confused. Why are we getting an out-of-bounds
> on a freed region? Is this a strange way of reporting access
> to already freed memory?

Hi Oliver,

This is being tracked in:
https://bugzilla.kernel.org/show_bug.cgi?id=198425