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Commit a1e89c8b authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman
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USB: core: Don't hold device lock while reading the "descriptors" sysfs file 



commit 45bf39f8df7f05efb83b302c65ae3b9bc92b7065 upstream.

Ever since commit 83e83ecb ("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: default avatarTroels Liebe Bentsen <troels@connectedcars.dk>
Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
CC: stable@vger.kernel.org
Link: https://lore.kernel.org/r/Y9l+wDTRbuZABzsE@rowland.harvard.edu


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 96d380d2

drivers/usb/core/hub.c

+2 −3
Original line number Diff line number Diff line
@@ -2379,9 +2379,8 @@ 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)

 *

 * 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

drivers/usb/core/sysfs.c

+0 −5
Original line number Diff line number Diff line
@@ -889,11 +889,7 @@ read_descriptors(struct file *filp, struct kobject *kobj, 
	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).
@@ -918,7 +914,6 @@ read_descriptors(struct file *filp, struct kobject *kobj, 
			off -= srclen;

		}

	}

	usb_unlock_device(udev);

	return count - nleft;

}