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 <[email protected]>
CC: Hans de Goede <[email protected]>
---
In theory, this could be applied to the stable kernels. In practice, I
doubt that it matters much.
[as1546]
drivers/usb/core/sysfs.c | 53 +++++++++++++++++++++++------------------------
1 file changed, 26 insertions(+), 27 deletions(-)
Index: usb-3.11/drivers/usb/core/sysfs.c
===================================================================
--- usb-3.11.orig/drivers/usb/core/sysfs.c
+++ usb-3.11/drivers/usb/core/sysfs.c
@@ -23,14 +23,16 @@ static ssize_t field##_show(struct devic
{ \
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 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
{
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, stru
* 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, stru
off -= srclen;
}
}
+ usb_unlock_device(udev);
return count - nleft;
}
@@ -870,9 +880,7 @@ static ssize_t interface_show(struct dev
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 devi
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_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);
--
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