Re: general protection fault in __pm_runtime_resume

Alan Stern
2019-08-15T17:43:38Z

On Mon, 12 Aug 2019, syzbot wrote:

> Hello,
>
> syzbot has tested the proposed patch and the reproducer did not trigger
> crash:
>
> Reported-and-tested-by:
> syzbot+3cbe5cd105d2ad56a1df@syzkaller.appspotmail.com
>
> Tested on:
>
> commit: 7f7867ff usb-fuzzer: main usb gadget fuzzer driver
> git tree: https://github.com/google/kasan.git
> kernel config: https://syzkaller.appspot.com/x/.config?x=792eb47789f57810
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> patch: https://syzkaller.appspot.com/x/patch.diff?x=177252d2600000
>
> Note: testing is done by a robot and is best-effort only.

That was the result from testing Hillf's patch:

--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -1410,6 +1410,7 @@ static void usbhid_disconnect(struct usb
spin_lock_irq(&usbhid->lock); /* Sync with error and led handlers */
set_bit(HID_DISCONNECTED, &usbhid->iofl);
spin_unlock_irq(&usbhid->lock);
+ hid_hw_stop(hid);
hid_destroy_device(hid);
kfree(usbhid);
}

There is very good reason to believe this patch is not the correct
solution to the problem. For one thing, in some circumstances the
patch ends up calling hid_hw_stop() twice (not shown here, but we have
seen this in other bug reports from syzbot).

For another, I have just tested a different patch and found that it
also prevents this particular crash:

> Hello,
>
> syzbot has tested the proposed patch and the reproducer did not trigger
> crash:
>
> Reported-and-tested-by:
> syzbot+3cbe5cd105d2ad56a1df@syzkaller.appspotmail.com
>
> Tested on:
>
> commit: 6a3599ce usb-fuzzer: main usb gadget fuzzer driver
> git tree: https://github.com/google/kasan.git
> kernel config: https://syzkaller.appspot.com/x/.config?x=700ca426ab83faae
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> patch: https://syzkaller.appspot.com/x/patch.diff?x=170b66a6600000
>
> Note: testing is done by a robot and is best-effort only.

My patch:

Index: usb-devel/drivers/hid/hid-lg.c
===================================================================
--- usb-devel.orig/drivers/hid/hid-lg.c
+++ usb-devel/drivers/hid/hid-lg.c
@@ -818,7 +818,7 @@ static int lg_probe(struct hid_device *h

if (!buf) {
ret = -ENOMEM;
- goto err_free;
+ goto err_stop;
}

ret = hid_hw_raw_request(hdev, buf[0], buf, sizeof(cbuf),
@@ -850,9 +850,12 @@ static int lg_probe(struct hid_device *h
ret = lg4ff_init(hdev);

if (ret)
- goto err_free;
+ goto err_stop;

return 0;
+
+err_stop:
+ hid_hw_stop(hdev);
err_free:
kfree(drv_data);
return ret;
@@ -863,8 +866,7 @@ static void lg_remove(struct hid_device
struct lg_drv_data *drv_data = hid_get_drvdata(hdev);
if (drv_data->quirks & LG_FF4)
lg4ff_deinit(hdev);
- else
- hid_hw_stop(hdev);
+ hid_hw_stop(hdev);
kfree(drv_data);
}

Index: usb-devel/drivers/hid/hid-lg4ff.c
===================================================================
--- usb-devel.orig/drivers/hid/hid-lg4ff.c
+++ usb-devel/drivers/hid/hid-lg4ff.c
@@ -1477,7 +1477,6 @@ int lg4ff_deinit(struct hid_device *hid)
}
}
#endif
- hid_hw_stop(hid);
drv_data->device_props = NULL;

kfree(entry);

This fixes a fairly obvious bug in the hid-lg driver: It does not
always call hid_hw_stop() in all pathways after calling hid_hw_start().

Presumably the same is true for the other related bugs found by syzbot.
I'm doing some more testing and we will see...

Alan Stern