linux/drivers/usb/core/file.c
Alan Stern d4ead16f50 USB: prevent char device open/deregister race
This patch (as908) adds central protection in usbcore for the
prototypical race between opening and unregistering a char device.
The spinlock used to protect the minor-numbers array is replaced with
an rwsem, which can remain locked across a call to a driver's open()
method.  This guarantees that open() and deregister() will be mutually
exclusive.

The private locks currently used in several individual drivers for
this purpose are no longer necessary, and the patch removes them.  The
following USB drivers are affected: usblcd, idmouse, auerswald,
legousbtower, sisusbvga/sisusb, ldusb, adutux, iowarrior, and
usb-skeleton.

As a side effect of this change, usb_deregister_dev() must not be
called while holding a lock that is acquired by open().  Unfortunately
a number of drivers do this, but luckily the solution is simple: call
usb_deregister_dev() before acquiring the lock.

In addition to these changes (and their consequent code
simplifications), the patch fixes a use-after-free bug in adutux and a
race between open() and release() in iowarrior.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2007-07-12 16:29:48 -07:00

248 lines
6 KiB
C

/*
* drivers/usb/core/file.c
*
* (C) Copyright Linus Torvalds 1999
* (C) Copyright Johannes Erdfelt 1999-2001
* (C) Copyright Andreas Gal 1999
* (C) Copyright Gregory P. Smith 1999
* (C) Copyright Deti Fliegl 1999 (new USB architecture)
* (C) Copyright Randy Dunlap 2000
* (C) Copyright David Brownell 2000-2001 (kernel hotplug, usb_device_id,
more docs, etc)
* (C) Copyright Yggdrasil Computing, Inc. 2000
* (usb_device_id matching changes by Adam J. Richter)
* (C) Copyright Greg Kroah-Hartman 2002-2003
*
*/
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/rwsem.h>
#include <linux/usb.h>
#include "usb.h"
#define MAX_USB_MINORS 256
static const struct file_operations *usb_minors[MAX_USB_MINORS];
static DECLARE_RWSEM(minor_rwsem);
static int usb_open(struct inode * inode, struct file * file)
{
int minor = iminor(inode);
const struct file_operations *c;
int err = -ENODEV;
const struct file_operations *old_fops, *new_fops = NULL;
down_read(&minor_rwsem);
c = usb_minors[minor];
if (!c || !(new_fops = fops_get(c)))
goto done;
old_fops = file->f_op;
file->f_op = new_fops;
/* Curiouser and curiouser... NULL ->open() as "no device" ? */
if (file->f_op->open)
err = file->f_op->open(inode,file);
if (err) {
fops_put(file->f_op);
file->f_op = fops_get(old_fops);
}
fops_put(old_fops);
done:
up_read(&minor_rwsem);
return err;
}
static const struct file_operations usb_fops = {
.owner = THIS_MODULE,
.open = usb_open,
};
static struct usb_class {
struct kref kref;
struct class *class;
} *usb_class;
static int init_usb_class(void)
{
int result = 0;
if (usb_class != NULL) {
kref_get(&usb_class->kref);
goto exit;
}
usb_class = kmalloc(sizeof(*usb_class), GFP_KERNEL);
if (!usb_class) {
result = -ENOMEM;
goto exit;
}
kref_init(&usb_class->kref);
usb_class->class = class_create(THIS_MODULE, "usb");
if (IS_ERR(usb_class->class)) {
result = IS_ERR(usb_class->class);
err("class_create failed for usb devices");
kfree(usb_class);
usb_class = NULL;
}
exit:
return result;
}
static void release_usb_class(struct kref *kref)
{
/* Ok, we cheat as we know we only have one usb_class */
class_destroy(usb_class->class);
kfree(usb_class);
usb_class = NULL;
}
static void destroy_usb_class(void)
{
if (usb_class)
kref_put(&usb_class->kref, release_usb_class);
}
int usb_major_init(void)
{
int error;
error = register_chrdev(USB_MAJOR, "usb", &usb_fops);
if (error)
err("unable to get major %d for usb devices", USB_MAJOR);
return error;
}
void usb_major_cleanup(void)
{
unregister_chrdev(USB_MAJOR, "usb");
}
/**
* usb_register_dev - register a USB device, and ask for a minor number
* @intf: pointer to the usb_interface that is being registered
* @class_driver: pointer to the usb_class_driver for this device
*
* This should be called by all USB drivers that use the USB major number.
* If CONFIG_USB_DYNAMIC_MINORS is enabled, the minor number will be
* dynamically allocated out of the list of available ones. If it is not
* enabled, the minor number will be based on the next available free minor,
* starting at the class_driver->minor_base.
*
* This function also creates a usb class device in the sysfs tree.
*
* usb_deregister_dev() must be called when the driver is done with
* the minor numbers given out by this function.
*
* Returns -EINVAL if something bad happens with trying to register a
* device, and 0 on success.
*/
int usb_register_dev(struct usb_interface *intf,
struct usb_class_driver *class_driver)
{
int retval = -EINVAL;
int minor_base = class_driver->minor_base;
int minor = 0;
char name[BUS_ID_SIZE];
char *temp;
#ifdef CONFIG_USB_DYNAMIC_MINORS
/*
* We don't care what the device tries to start at, we want to start
* at zero to pack the devices into the smallest available space with
* no holes in the minor range.
*/
minor_base = 0;
#endif
intf->minor = -1;
dbg ("looking for a minor, starting at %d", minor_base);
if (class_driver->fops == NULL)
goto exit;
down_write(&minor_rwsem);
for (minor = minor_base; minor < MAX_USB_MINORS; ++minor) {
if (usb_minors[minor])
continue;
usb_minors[minor] = class_driver->fops;
retval = 0;
break;
}
up_write(&minor_rwsem);
if (retval)
goto exit;
retval = init_usb_class();
if (retval)
goto exit;
intf->minor = minor;
/* create a usb class device for this usb interface */
snprintf(name, BUS_ID_SIZE, class_driver->name, minor - minor_base);
temp = strrchr(name, '/');
if (temp && (temp[1] != 0x00))
++temp;
else
temp = name;
intf->usb_dev = device_create(usb_class->class, &intf->dev,
MKDEV(USB_MAJOR, minor), "%s", temp);
if (IS_ERR(intf->usb_dev)) {
down_write(&minor_rwsem);
usb_minors[intf->minor] = NULL;
up_write(&minor_rwsem);
retval = PTR_ERR(intf->usb_dev);
}
exit:
return retval;
}
EXPORT_SYMBOL(usb_register_dev);
/**
* usb_deregister_dev - deregister a USB device's dynamic minor.
* @intf: pointer to the usb_interface that is being deregistered
* @class_driver: pointer to the usb_class_driver for this device
*
* Used in conjunction with usb_register_dev(). This function is called
* when the USB driver is finished with the minor numbers gotten from a
* call to usb_register_dev() (usually when the device is disconnected
* from the system.)
*
* This function also removes the usb class device from the sysfs tree.
*
* This should be called by all drivers that use the USB major number.
*/
void usb_deregister_dev(struct usb_interface *intf,
struct usb_class_driver *class_driver)
{
int minor_base = class_driver->minor_base;
char name[BUS_ID_SIZE];
#ifdef CONFIG_USB_DYNAMIC_MINORS
minor_base = 0;
#endif
if (intf->minor == -1)
return;
dbg ("removing %d minor", intf->minor);
down_write(&minor_rwsem);
usb_minors[intf->minor] = NULL;
up_write(&minor_rwsem);
snprintf(name, BUS_ID_SIZE, class_driver->name, intf->minor - minor_base);
device_destroy(usb_class->class, MKDEV(USB_MAJOR, intf->minor));
intf->usb_dev = NULL;
intf->minor = -1;
destroy_usb_class();
}
EXPORT_SYMBOL(usb_deregister_dev);