Greg: 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. Alan Stern Signed-off-by: Alan Stern <[EMAIL PROTECTED]> --- Index: usb-2.6/drivers/usb/core/devio.c =================================================================== --- usb-2.6.orig/drivers/usb/core/devio.c +++ usb-2.6/drivers/usb/core/devio.c @@ -58,6 +58,9 @@ #define USB_DEVICE_MAX USB_MAXBUS * 128 static struct class *usb_device_class; +/* Mutual exclusion for removal, open, and release */ +DEFINE_MUTEX(usbfs_mutex); + struct async { struct list_head asynclist; struct dev_state *ps; @@ -539,15 +542,13 @@ static int usbdev_open(struct inode *ino 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) @@ -576,9 +577,8 @@ static int usbdev_open(struct inode *ino list_add_tail(&ps->list, &dev->filelist); file->private_data = ps; out: - unlock_kernel(); - out_nolock: - return ret; + mutex_unlock(&usbfs_mutex); + return ret; } static int usbdev_release(struct inode *inode, struct file *file) @@ -588,7 +588,12 @@ static int usbdev_release(struct inode * unsigned int ifnum; usb_lock_device(dev); + + /* Protect against simultaneous open */ + mutex_lock(&usbfs_mutex); list_del_init(&ps->list); + mutex_unlock(&usbfs_mutex); + for (ifnum = 0; ps->ifclaimed && ifnum < 8*sizeof(ps->ifclaimed); ifnum++) { if (test_bit(ifnum, &ps->ifclaimed)) @@ -597,9 +602,8 @@ static int usbdev_release(struct inode * destroy_all_async(ps); usb_unlock_device(dev); usb_put_dev(dev); - ps->dev = NULL; kfree(ps); - return 0; + return 0; } static int proc_control(struct dev_state *ps, void __user *arg) Index: usb-2.6/drivers/usb/core/usb.h =================================================================== --- usb-2.6.orig/drivers/usb/core/usb.h +++ usb-2.6/drivers/usb/core/usb.h @@ -59,6 +59,7 @@ static inline int is_active(struct usb_i 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; Index: usb-2.6/drivers/usb/core/notify.c =================================================================== --- usb-2.6.orig/drivers/usb/core/notify.c +++ usb-2.6/drivers/usb/core/notify.c @@ -51,8 +51,11 @@ void usb_notify_add_device(struct usb_de void usb_notify_remove_device(struct usb_device *udev) { + /* Protect against simultaneous usbfs open */ + mutex_lock(&usbfs_mutex); blocking_notifier_call_chain(&usb_notifier_list, USB_DEVICE_REMOVE, udev); + mutex_unlock(&usbfs_mutex); } void usb_notify_add_bus(struct usb_bus *ubus) _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel