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USB: cdc-wdm: Make wdm_flush() interruptible and add wdm_fsync().

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syzbot is reporting hung task at wdm_flush() [1], for there is a circular
dependency that wdm_flush() from flip_close() for /dev/cdc-wdm0 forever
waits for /dev/raw-gadget to be closed while close() for /dev/raw-gadget
cannot be called unless close() for /dev/cdc-wdm0 completes.

Tetsuo Handa considered that such circular dependency is an usage error [2]
which corresponds to an unresponding broken hardware [3]. But Alan Stern
responded that we should be prepared for such hardware [4]. Therefore,
this patch changes wdm_flush() to use wait_event_interruptible_timeout()
which gives up after 30 seconds, for hardware that remains silent must be
ignored. The 30 seconds are coming out of thin air.

Changing wait_event() to wait_event_interruptible_timeout() makes error
reporting from close() syscall less reliable. To compensate it, this patch
also implements wdm_fsync() which does not use timeout. Those who want to
be very sure that data has gone out to the device are now advised to call
fsync(), with a caveat that fsync() can return -EINVAL when running on
older kernels which do not implement wdm_fsync().

This patch also fixes three more problems (listed below) found during
exhaustive discussion and testing.

  Since multiple threads can concurrently call wdm_write()/wdm_flush(),
  we need to use wake_up_all() whenever clearing WDM_IN_USE in order to
  make sure that all waiters are woken up. Also, error reporting needs
  to use fetch-and-clear approach in order not to report same error for
  multiple times.

  Since wdm_flush() checks WDM_DISCONNECTING, wdm_write() should as well
  check WDM_DISCONNECTING.

  In wdm_flush(), since locks are not held, it is not safe to dereference
  desc->intf after checking that WDM_DISCONNECTING is not set [5]. Thus,
  remove dev_err() from wdm_flush().

[1] https://syzkaller.appspot.com/bug?id=e7b761593b23eb50855b9ea31e3be5472b711186
[2] https://lkml.kernel.org/r/27b7545e-8f41-10b8-7c02-e35a08eb1611@i-love.sakura.ne.jp
[3] https://lkml.kernel.org/r/79ba410f-e0ef-2465-b94f-6b9a4a82adf5@i-love.sakura.ne.jp
[4] https://lkml.kernel.org/r/20200530011040.GB12419@rowland.harvard.edu
[5] https://lkml.kernel.org/r/c85331fc-874c-6e46-a77f-0ef1dc075308@i-love.sakura.ne.jp

Reported-by: syzbot <syzbot+854768b99f19e89d7f81@syzkaller.appspotmail.com>
Cc: stable <stable@vger.kernel.org>
Co-developed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20200928141755.3476-1-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Oliver Neukum 2020-09-28 23:17:55 +09:00 committed by Greg Kroah-Hartman
parent fb58cf4f28
commit 37d2a36394
1 changed files with 54 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
drivers/usb/class/cdc-wdm.c
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@ -58,6 +58,9 @@ MODULE_DEVICE_TABLE (usb, wdm_ids);
#define WDM_MAX 16
/* we cannot wait forever at flush() */
#define WDM_FLUSH_TIMEOUT (30 * HZ)
/* CDC-WMC r1.1 requires wMaxCommand to be "at least 256 decimal (0x100)" */
#define WDM_DEFAULT_BUFSIZE 256
@ -151,7 +154,7 @@ static void wdm_out_callback(struct urb *urb)
kfree(desc->outbuf);
desc->outbuf = NULL;
clear_bit(WDM_IN_USE, &desc->flags);
wake_up(&desc->wait);
wake_up_all(&desc->wait);
}
static void wdm_in_callback(struct urb *urb)
@ -393,6 +396,9 @@ static ssize_t wdm_write
if (test_bit(WDM_RESETTING, &desc->flags))
r = -EIO;
if (test_bit(WDM_DISCONNECTING, &desc->flags))
r = -ENODEV;
if (r < 0) {
rv = r;
goto out_free_mem_pm;
@ -424,6 +430,7 @@ static ssize_t wdm_write
if (rv < 0) {
desc->outbuf = NULL;
clear_bit(WDM_IN_USE, &desc->flags);
wake_up_all(&desc->wait); /* for wdm_wait_for_response() */
dev_err(&desc->intf->dev, "Tx URB error: %d\n", rv);
rv = usb_translate_errors(rv);
goto out_free_mem_pm;
@ -583,28 +590,58 @@ static ssize_t wdm_read
return rv;
}
static int wdm_flush(struct file *file, fl_owner_t id)
static int wdm_wait_for_response(struct file *file, long timeout)
{
struct wdm_device *desc = file->private_data;
long rv; /* Use long here because (int) MAX_SCHEDULE_TIMEOUT < 0. */
wait_event(desc->wait,
/*
* needs both flags. We cannot do with one
* because resetting it would cause a race
* with write() yet we need to signal
* a disconnect
*/
!test_bit(WDM_IN_USE, &desc->flags) ||
test_bit(WDM_DISCONNECTING, &desc->flags));
/*
* Needs both flags. We cannot do with one because resetting it would
* cause a race with write() yet we need to signal a disconnect.
*/
rv = wait_event_interruptible_timeout(desc->wait,
!test_bit(WDM_IN_USE, &desc->flags) ||
test_bit(WDM_DISCONNECTING, &desc->flags),
timeout);
/* cannot dereference desc->intf if WDM_DISCONNECTING */
/*
* To report the correct error. This is best effort.
* We are inevitably racing with the hardware.
*/
if (test_bit(WDM_DISCONNECTING, &desc->flags))
return -ENODEV;
if (desc->werr < 0)
dev_err(&desc->intf->dev, "Error in flush path: %d\n",
desc->werr);
if (!rv)
return -EIO;
if (rv < 0)
return -EINTR;
return usb_translate_errors(desc->werr);
spin_lock_irq(&desc->iuspin);
rv = desc->werr;
desc->werr = 0;
spin_unlock_irq(&desc->iuspin);
return usb_translate_errors(rv);
}
/*
* You need to send a signal when you react to malicious or defective hardware.
* Also, don't abort when fsync() returned -EINVAL, for older kernels which do
* not implement wdm_flush() will return -EINVAL.
*/
static int wdm_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
return wdm_wait_for_response(file, MAX_SCHEDULE_TIMEOUT);
}
/*
* Same with wdm_fsync(), except it uses finite timeout in order to react to
* malicious or defective hardware which ceased communication after close() was
* implicitly called due to process termination.
*/
static int wdm_flush(struct file *file, fl_owner_t id)
{
return wdm_wait_for_response(file, WDM_FLUSH_TIMEOUT);
}
static __poll_t wdm_poll(struct file *file, struct poll_table_struct *wait)
@ -729,6 +766,7 @@ static const struct file_operations wdm_fops = {
.owner = THIS_MODULE,
.read = wdm_read,
.write = wdm_write,
.fsync = wdm_fsync,
.open = wdm_open,
.flush = wdm_flush,
.release = wdm_release,