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authorAlan Stern <stern@rowland.harvard.edu>2006-07-01 22:05:01 -0400
committerChris Wright <chrisw@sous-sol.org>2006-11-03 17:33:50 -0800
commit108d51a5710a51ed46353655efc7d165b4c57b60 (patch)
parent3b076a9455026e5d736aeff6ca02a95972dff417 (diff)
[PATCH] usbfs: private mutex for open, release, and remove
The usbfs code doesn't provide sufficient mutual exclusion among open, release, and remove. Release vs. remove is okay because they both acquire the device lock, but open is not exclusive with either one. All three routines modify the udev->filelist linked list, so they must not run concurrently. Apparently someone gave this a minimum amount of thought in the past by explicitly acquiring the BKL at the start of the usbdev_open routine. Oddly enough, there's a comment pointing out that locking is unnecessary because chrdev_open already has acquired the BKL. But this ignores the point that the files in /proc/bus/usb/* are not char device files; they are regular files and so they don't get any special locking. Furthermore it's necessary to acquire the same lock in the release and remove routines, which the code does not do. Yet another problem arises because the same file_operations structure is accessible through both the /proc/bus/usb/* and /dev/usb/usbdev* file nodes. Even when one of them has been removed, it's still possible for userspace to open the other. So simple locking around the individual remove routines is insufficient; we need to lock the entire usb_notify_remove_device notifier chain. Rather than rely on the BKL, this patch (as723) introduces a new private mutex for the purpose. Holding the BKL while invoking a notifier chain doesn't seem like a good idea. Cc: Dave Jones <davej@redhat.com> [https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=212952] Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Chris Wright <chrisw@sous-sol.org>
3 files changed, 19 insertions, 11 deletions
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 218621b9958e..ab6cc03a670b 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -59,6 +59,9 @@
static struct class *usb_device_class;
+/* Mutual exclusion for removal, open, and release */
struct async {
struct list_head asynclist;
struct dev_state *ps;
@@ -541,15 +544,13 @@ static int usbdev_open(struct inode *inode, struct file *file)
struct dev_state *ps;
int ret;
- /*
- * no locking necessary here, as chrdev_open has the kernel lock
- * (still acquire the kernel lock for safety)
- */
+ /* Protect against simultaneous removal or release */
+ mutex_lock(&usbfs_mutex);
ret = -ENOMEM;
if (!(ps = kmalloc(sizeof(struct dev_state), GFP_KERNEL)))
- goto out_nolock;
+ goto out;
- lock_kernel();
ret = -ENOENT;
/* check if we are called from a real node or usbfs */
if (imajor(inode) == USB_DEVICE_MAJOR)
@@ -579,9 +580,8 @@ static int usbdev_open(struct inode *inode, struct file *file)
list_add_tail(&ps->list, &dev->filelist);
file->private_data = ps;
- unlock_kernel();
- out_nolock:
- return ret;
+ mutex_unlock(&usbfs_mutex);
+ return ret;
static int usbdev_release(struct inode *inode, struct file *file)
@@ -591,7 +591,12 @@ static int usbdev_release(struct inode *inode, struct file *file)
unsigned int ifnum;
+ /* Protect against simultaneous open */
+ mutex_lock(&usbfs_mutex);
+ mutex_unlock(&usbfs_mutex);
for (ifnum = 0; ps->ifclaimed && ifnum < 8*sizeof(ps->ifclaimed);
ifnum++) {
if (test_bit(ifnum, &ps->ifclaimed))
@@ -600,9 +605,8 @@ static int usbdev_release(struct inode *inode, struct file *file)
- ps->dev = NULL;
- return 0;
+ return 0;
static int proc_control(struct dev_state *ps, void __user *arg)
diff --git a/drivers/usb/core/notify.c b/drivers/usb/core/notify.c
index b042676af0a5..6b36897ca151 100644
--- a/drivers/usb/core/notify.c
+++ b/drivers/usb/core/notify.c
@@ -50,8 +50,11 @@ void usb_notify_add_device(struct usb_device *udev)
void usb_notify_remove_device(struct usb_device *udev)
+ /* Protect against simultaneous usbfs open */
+ mutex_lock(&usbfs_mutex);
+ mutex_unlock(&usbfs_mutex);
void usb_notify_add_bus(struct usb_bus *ubus)
diff --git a/drivers/usb/core/usb.h b/drivers/usb/core/usb.h
index 49f69236b420..1217fbbe5829 100644
--- a/drivers/usb/core/usb.h
+++ b/drivers/usb/core/usb.h
@@ -59,6 +59,7 @@ static inline int is_active(struct usb_interface *f)
extern const char *usbcore_name;
/* usbfs stuff */
+extern struct mutex usbfs_mutex;
extern struct usb_driver usbfs_driver;
extern struct file_operations usbfs_devices_fops;
extern struct file_operations usbfs_device_file_operations;