USB: fix substandard locking for the sysfs files

This patch straightens out some locking issues in the USB sysfs
interface:

	Deauthorization will destroy existing configurations.
	Attributes that read from udev->actconfig need to lock the
	device to prevent races.  Likewise for the rawdescriptor
	values.

	Attributes that access an interface's current alternate
	setting should use ACCESS_ONCE() to obtain the cur_altsetting
	pointer, to protect against concurrent altsetting changes.

	The supports_autosuspend() attribute routine accesses values
	from an interface's driver, so it should lock the interface
	(rather than the usb_device) to protect against concurrent
	unbinds.  Once this is done, the routine can be simplified
	considerably.

Scalar values that are stored directly in the usb_device structure are
always available.  They do not require any locking.  The same is true
of the cached interface string descriptor, because it is not
deallocated until the usb_host_interface structure is destroyed.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index 6d2c8ed..59cb5f9 100644 (file)
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -23,14 +23,16 @@ static ssize_t field##_show(struct device *dev,                             \
 {                                                                      \
        struct usb_device *udev;                                        \
        struct usb_host_config *actconfig;                              \
+       ssize_t rc = 0;                                                 \
                                                                        \
        udev = to_usb_device(dev);                                      \
+       usb_lock_device(udev);                                          \
        actconfig = udev->actconfig;                                    \
        if (actconfig)                                                  \
-               return sprintf(buf, format_string,                      \
+               rc = sprintf(buf, format_string,                        \
                                actconfig->desc.field);                 \
-       else                                                            \
-               return 0;                                               \
+       usb_unlock_device(udev);                                        \
+       return rc;                                                      \
 }                                                                      \
 
 #define usb_actconfig_attr(field, format_string)               \
@@ -45,12 +47,15 @@ static ssize_t bMaxPower_show(struct device *dev,
 {
        struct usb_device *udev;
        struct usb_host_config *actconfig;
+       ssize_t rc = 0;
 
        udev = to_usb_device(dev);
+       usb_lock_device(udev);
        actconfig = udev->actconfig;
-       if (!actconfig)
-               return 0;
-       return sprintf(buf, "%dmA\n", usb_get_max_power(udev, actconfig));
+       if (actconfig)
+               rc = sprintf(buf, "%dmA\n", usb_get_max_power(udev, actconfig));
+       usb_unlock_device(udev);
+       return rc;
 }
 static DEVICE_ATTR_RO(bMaxPower);
 
@@ -59,12 +64,15 @@ static ssize_t configuration_show(struct device *dev,
 {
        struct usb_device *udev;
        struct usb_host_config *actconfig;
+       ssize_t rc = 0;
 
        udev = to_usb_device(dev);
+       usb_lock_device(udev);
        actconfig = udev->actconfig;
-       if ((!actconfig) || (!actconfig->string))
-               return 0;
-       return sprintf(buf, "%s\n", actconfig->string);
+       if (actconfig && actconfig->string)
+               rc = sprintf(buf, "%s\n", actconfig->string);
+       usb_unlock_device(udev);
+       return rc;
 }
 static DEVICE_ATTR_RO(configuration);
 
@@ -764,6 +772,7 @@ read_descriptors(struct file *filp, struct kobject *kobj,
         * Following that are the raw descriptor entries for all the
         * configurations (config plus subsidiary descriptors).
         */
+       usb_lock_device(udev);
        for (cfgno = -1; cfgno < udev->descriptor.bNumConfigurations &&
                        nleft > 0; ++cfgno) {
                if (cfgno < 0) {
@@ -784,6 +793,7 @@ read_descriptors(struct file *filp, struct kobject *kobj,
                        off -= srclen;
                }
        }
+       usb_unlock_device(udev);
        return count - nleft;
 }
 
@@ -870,9 +880,7 @@ static ssize_t interface_show(struct device *dev, struct device_attribute *attr,
        char *string;
 
        intf = to_usb_interface(dev);
-       string = intf->cur_altsetting->string;
-       barrier();              /* The altsetting might change! */
-
+       string = ACCESS_ONCE(intf->cur_altsetting->string);
        if (!string)
                return 0;
        return sprintf(buf, "%s\n", string);
@@ -888,7 +896,7 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 
        intf = to_usb_interface(dev);
        udev = interface_to_usbdev(intf);
-       alt = intf->cur_altsetting;
+       alt = ACCESS_ONCE(intf->cur_altsetting);
 
        return sprintf(buf, "usb:v%04Xp%04Xd%04Xdc%02Xdsc%02Xdp%02X"
                        "ic%02Xisc%02Xip%02Xin%02X\n",
@@ -909,23 +917,14 @@ static ssize_t supports_autosuspend_show(struct device *dev,
                                         struct device_attribute *attr,
                                         char *buf)
 {
-       struct usb_interface *intf;
-       struct usb_device *udev;
-       int ret;
+       int s;
 
-       intf = to_usb_interface(dev);
-       udev = interface_to_usbdev(intf);
-
-       usb_lock_device(udev);
+       device_lock(dev);
        /* Devices will be autosuspended even when an interface isn't claimed */
-       if (!intf->dev.driver ||
-                       to_usb_driver(intf->dev.driver)->supports_autosuspend)
-               ret = sprintf(buf, "%u\n", 1);
-       else
-               ret = sprintf(buf, "%u\n", 0);
-       usb_unlock_device(udev);
+       s = (!dev->driver || to_usb_driver(dev->driver)->supports_autosuspend);
+       device_unlock(dev);
 
-       return ret;
+       return sprintf(buf, "%u\n", s);
 }
 static DEVICE_ATTR_RO(supports_autosuspend);