[PATCH 1/1] UBUNTU: SAUCE: khubd -- switch USB product/manufacturer/serial handling to RCU

Andy Whitcroft apw at canonical.com
Wed Feb 17 17:37:05 UTC 2010


BugLink: http://bugs.launchpad.net/bugs/510937

With the introduction of wireless USB hubs the product, manufacturer,
and serial number are now mutable.  This necessitates new locking in the
consumers of these values including the sysfs read routines in order to
prevent use-after-free acces to these values.  These extra locks create
significant lock contention leading to increased boot times (0.3s for an
example Atom based system).  Move update of these values to RCU based
locking.

Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 drivers/usb/core/hub.c   |   34 ++++++++++++++++++++++++++++------
 drivers/usb/core/sysfs.c |    6 +++---
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 1a7d54b..75804a9 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -22,6 +22,7 @@
 #include <linux/kthread.h>
 #include <linux/mutex.h>
 #include <linux/freezer.h>
+#include <linux/rcupdate.h>
 
 #include <asm/uaccess.h>
 #include <asm/byteorder.h>
@@ -1803,6 +1804,10 @@ fail:
  */
 int usb_deauthorize_device(struct usb_device *usb_dev)
 {
+	char *product = NULL;
+	char *manufacturer = NULL;
+	char *serial = NULL;
+
 	usb_lock_device(usb_dev);
 	if (usb_dev->authorized == 0)
 		goto out_unauthorized;
@@ -1810,11 +1815,12 @@ int usb_deauthorize_device(struct usb_device *usb_dev)
 	usb_dev->authorized = 0;
 	usb_set_configuration(usb_dev, -1);
 
-	kfree(usb_dev->product);
+	product = usb_dev->product;
+	manufacturer = usb_dev->manufacturer;
+	serial = usb_dev->serial;
+
 	usb_dev->product = kstrdup("n/a (unauthorized)", GFP_KERNEL);
-	kfree(usb_dev->manufacturer);
 	usb_dev->manufacturer = kstrdup("n/a (unauthorized)", GFP_KERNEL);
-	kfree(usb_dev->serial);
 	usb_dev->serial = kstrdup("n/a (unauthorized)", GFP_KERNEL);
 
 	usb_destroy_configuration(usb_dev);
@@ -1822,6 +1828,12 @@ int usb_deauthorize_device(struct usb_device *usb_dev)
 
 out_unauthorized:
 	usb_unlock_device(usb_dev);
+	if (product || manufacturer || serial) {
+		synchronize_rcu();
+		kfree(product);
+		kfree(manufacturer);
+		kfree(serial);
+	}
 	return 0;
 }
 
@@ -1829,6 +1841,9 @@ out_unauthorized:
 int usb_authorize_device(struct usb_device *usb_dev)
 {
 	int result = 0, c;
+	char *product = NULL;
+	char *manufacturer = NULL;
+	char *serial = NULL;
 
 	usb_lock_device(usb_dev);
 	if (usb_dev->authorized == 1)
@@ -1847,11 +1862,12 @@ int usb_authorize_device(struct usb_device *usb_dev)
 		goto error_device_descriptor;
 	}
 
-	kfree(usb_dev->product);
+	
+	product = usb_dev->product;
 	usb_dev->product = NULL;
-	kfree(usb_dev->manufacturer);
+	manufacturer = usb_dev->manufacturer;
 	usb_dev->manufacturer = NULL;
-	kfree(usb_dev->serial);
+	serial = usb_dev->serial;
 	usb_dev->serial = NULL;
 
 	usb_dev->authorized = 1;
@@ -1879,6 +1895,12 @@ error_device_descriptor:
 error_autoresume:
 out_authorized:
 	usb_unlock_device(usb_dev);	// complements locktree
+	if (product || manufacturer || serial) {
+		synchronize_rcu();
+		kfree(product);
+		kfree(manufacturer);
+		kfree(serial);
+	}
 	return result;
 }
 
diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index fcdcad4..25d2fa7 100644
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -85,9 +85,9 @@ static ssize_t  show_##name(struct device *dev,				\
 	int retval;							\
 									\
 	udev = to_usb_device(dev);					\
-	usb_lock_device(udev);						\
-	retval = sprintf(buf, "%s\n", udev->name);			\
-	usb_unlock_device(udev);					\
+	rcu_read_lock();						\
+	retval = sprintf(buf, "%s\n", rcu_dereference(udev->name));	\
+	rcu_read_unlock();						\
 	return retval;							\
 }									\
 static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL);
-- 
1.6.6.1





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