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

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 9eca403af2a85bf4541a74e69ebee75ddaa42c61..97a0f8faea6e5ff33ee9b695850c13c5c8e7f657 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)
  *
- * 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

diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index 8217032dfb85fa27200c1812ae068f317995494e..b63f78e48c74efabe3818d04b0238afae3ed6048 100644 (file)
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -869,11 +869,7 @@ 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).
@@ -898,7 +894,6 @@ read_descriptors(struct file *filp, struct kobject *kobj,
                        off -= srclen;
                }
        }
-       usb_unlock_device(udev);
        return count - nleft;
 }