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SubjectRe: WARNING in usbhid_raw_request/usb_submit_urb
On Mon, 12 Aug 2019, syzbot wrote:

> Hello,
>
> syzbot has tested the proposed patch but the reproducer still triggered
> crash:
> KASAN: invalid-free in hcd_buffer_free

This bug report shows that Hillf's fix isn't exactly right.

> usb 5-1: USB disconnect, device number 2
> ==================================================================
> BUG: KASAN: double-free or invalid-free in hcd_buffer_free+0x199/0x260
> drivers/usb/core/buffer.c:165
>
> CPU: 0 PID: 1745 Comm: kworker/0:2 Not tainted 5.3.0-rc2+ #1
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: usb_hub_wq hub_event
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0xca/0x13e lib/dump_stack.c:113
> print_address_description+0x6a/0x32c mm/kasan/report.c:351
> kasan_report_invalid_free+0x61/0xa0 mm/kasan/report.c:444
> __kasan_slab_free+0x162/0x180 mm/kasan/common.c:428
> slab_free_hook mm/slub.c:1423 [inline]
> slab_free_freelist_hook mm/slub.c:1470 [inline]
> slab_free mm/slub.c:3012 [inline]
> kfree+0xe4/0x2f0 mm/slub.c:3953
> hcd_buffer_free+0x199/0x260 drivers/usb/core/buffer.c:165
> usb_free_coherent+0x67/0x80 drivers/usb/core/usb.c:932
> hid_free_buffers.isra.0+0x94/0x290 drivers/hid/usbhid/hid-core.c:964
> usbhid_stop+0x308/0x450 drivers/hid/usbhid/hid-core.c:1224
> logi_dj_remove+0x107/0x210 drivers/hid/hid-logitech-dj.c:1797

Here the double-free occurred when logi_dj_remove() called
hd_hw_stop()...

> hid_device_remove+0xed/0x240 drivers/hid/hid-core.c:2242
> __device_release_driver drivers/base/dd.c:1118 [inline]
> device_release_driver_internal+0x206/0x4c0 drivers/base/dd.c:1151
> bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:556
> device_del+0x420/0xb10 drivers/base/core.c:2288
> hid_remove_device drivers/hid/hid-core.c:2413 [inline]
> hid_destroy_device+0xe1/0x150 drivers/hid/hid-core.c:2432
> usbhid_disconnect+0xad/0xd0 drivers/hid/usbhid/hid-core.c:1414

which occurred inside usbhid_disconnect()'s call to
hid_destroy_device().

But just above the call to hid_destroy_device(), Hillf's patch adds a
direct call to hid_hw_stop(), which is what did the original free.

So it looks like the problem here is that some paths in the original
unpatched code end up calling hid_hw_stop() by way of the hid_device's
driver, and other paths do not.

I haven't had time to track down this difference. Maybe somebody
on the mailing list already knows why it occurs.

Alan Stern

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