USB: core: Don't hold device lock while reading the "descriptors" sysfs file

commit 45bf39f8df7f05efb83b302c65ae3b9bc92b7065 upstream.

Ever since commit 83e83ecb79a8 ("usb: core: get config and string
descriptors for unauthorized devices") was merged in 2013, there has
been no mechanism for reallocating the rawdescriptors buffers in
struct usb_device after the initial enumeration.  Before that commit,
the buffers would be deallocated when a device was deauthorized and
reallocated when it was authorized and enumerated.

This means that the locking in the read_descriptors() routine is not
needed, since the buffers it reads will never be reallocated while the
routine is running.  This locking can interfere with user programs
trying to read a hub's descriptors via sysfs while new child devices
of the hub are being initialized, since the hub is locked during this
procedure.

Since the locking in read_descriptors() hasn't been needed for over
nine years, we can remove it.

Reported-and-tested-by: Troels Liebe Bentsen <troels@connectedcars.dk>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: stable@vger.kernel.org
Link: https://lore.kernel.org/r/Y9l+wDTRbuZABzsE@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 0aaaadb..1abe43d 100644 (file)
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2389,9 +2389,8 @@ static int usb_enumerate_device_otg(struct usb_device *udev)
  * usb_enumerate_device - Read device configs/intfs/otg (usbcore-internal)
  * @udev: newly addressed device (in ADDRESS state)
  *
  * usb_enumerate_device - Read device configs/intfs/otg (usbcore-internal)
  * @udev: newly addressed device (in ADDRESS state)
  *

- * This is only called by usb_new_device() and usb_authorize_device()
- * and FIXME -- all comments that apply to them apply here wrt to
- * environment.
+ * This is only called by usb_new_device() -- all comments that apply there
+ * apply here wrt to environment.

  *
  * If the device is WUSB and not authorized, we don't attempt to read
  * the string descriptors, as they will be errored out by the device
  *
  * If the device is WUSB and not authorized, we don't attempt to read
  * the string descriptors, as they will be errored out by the device

diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index 6315747..ccf6cd9 100644 (file)
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -868,11 +868,7 @@ read_descriptors(struct file *filp, struct kobject *kobj,
        size_t srclen, n;
        int cfgno;
        void *src;
        size_t srclen, n;
        int cfgno;
        void *src;

-       int retval;

 
 

-       retval = usb_lock_device_interruptible(udev);
-       if (retval < 0)
-               return -EINTR;

        /* The binary attribute begins with the device descriptor.
         * Following that are the raw descriptor entries for all the
         * configurations (config plus subsidiary descriptors).
        /* The binary attribute begins with the device descriptor.
         * Following that are the raw descriptor entries for all the
         * configurations (config plus subsidiary descriptors).


@@ -897,7 +893,6 @@ read_descriptors(struct file *filp, struct kobject *kobj,
                        off -= srclen;
                }
        }
                        off -= srclen;
                }
        }

-       usb_unlock_device(udev);

        return count - nleft;
 }
 
        return count - nleft;
 }