patch "usb: f_fs: Avoid crash due to out-of-scope stack ptr access" added to usb-next

patch "usb: f_fs: Avoid crash due to out-of-scope stack ptr access" added to usb-next

[Greg Kroah-Hartman]

This is a note to let you know that I've just added the patch titled

    usb: f_fs: Avoid crash due to out-of-scope stack ptr access

to my usb git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.


From 54f64d5c983f939901dacc8cfc0983727c5c742e Mon Sep 17 00:00:00 2001
From: John Stultz <john.stultz@linaro.org>
Date: Tue, 5 Feb 2019 10:24:40 -0800
Subject: usb: f_fs: Avoid crash due to out-of-scope stack ptr access

Since the 5.0 merge window opened, I've been seeing frequent
crashes on suspend and reboot with the trace:

[   36.911170] Unable to handle kernel paging request at virtual address ffffff801153d660
[   36.912769] Unable to handle kernel paging request at virtual address ffffff800004b564
...
[   36.950666] Call trace:
[   36.950670]  queued_spin_lock_slowpath+0x1cc/0x2c8
[   36.950681]  _raw_spin_lock_irqsave+0x64/0x78
[   36.950692]  complete+0x28/0x70
[   36.950703]  ffs_epfile_io_complete+0x3c/0x50
[   36.950713]  usb_gadget_giveback_request+0x34/0x108
[   36.950721]  dwc3_gadget_giveback+0x50/0x68
[   36.950723]  dwc3_thread_interrupt+0x358/0x1488
[   36.950731]  irq_thread_fn+0x30/0x88
[   36.950734]  irq_thread+0x114/0x1b0
[   36.950739]  kthread+0x104/0x130
[   36.950747]  ret_from_fork+0x10/0x1c

I isolated this down to in ffs_epfile_io():
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/gadget/function/f_fs.c#n1065

Where the completion done is setup on the stack:
  DECLARE_COMPLETION_ONSTACK(done);

Then later we setup a request and queue it, and wait for it:
  if (unlikely(wait_for_completion_interruptible(&done))) {
    /*
    * To avoid race condition with ffs_epfile_io_complete,
    * dequeue the request first then check
    * status. usb_ep_dequeue API should guarantee no race
    * condition with req->complete callback.
    */
    usb_ep_dequeue(ep->ep, req);
    interrupted = ep->status < 0;
  }

The problem is, that we end up being interrupted, dequeue the
request, and exit.

But then the irq triggers and we try calling complete() on the
context pointer which points to now random stack space, which
results in the panic.

Alan Stern pointed out there is a bug here, in that the snippet
above "assumes that usb_ep_dequeue() waits until the request has
been completed." And that:

    wait_for_completion(&done);

Is needed right after the usb_ep_dequeue().

Thus this patch implements that change. With it I no longer see
the crashes on suspend or reboot.

This issue seems to have been uncovered by behavioral changes in
the dwc3 driver in commit fec9095bdef4e ("usb: dwc3: gadget:
remove wait_end_transfer").

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Zeng Tao <prime.zeng@hisilicon.com>
Cc: Jack Pham <jackp@codeaurora.org>
Cc: Thinh Nguyen <thinh.nguyen@synopsys.com>
Cc: Chen Yu <chenyu56@huawei.com>
Cc: Jerry Zhang <zhangjerry@google.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Vincent Pelletier <plr.vincent@gmail.com>
Cc: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linux USB List <linux-usb@vger.kernel.org>
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
---
 drivers/usb/gadget/function/f_fs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 66a2c165b4b7..20413c276c61 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1082,6 +1082,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 			 * condition with req->complete callback.
 			 */
 			usb_ep_dequeue(ep->ep, req);
+			wait_for_completion(&done);
 			interrupted = ep->status < 0;
 		}