/* * access.c -- the files with access control on open * * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet * Copyright (C) 2001 O'Reilly & Associates * * The source code in this file can be freely used, adapted, * and redistributed in source or binary form, so long as an * acknowledgment appears in derived source files.  The citation * should list that the code comes from the book "Linux Device * Drivers" by Alessandro Rubini and Jonathan Corbet, published * by O'Reilly & Associates.   No warranty is attached; * we cannot take responsibility for errors or fitness for use. * * $Id: access.c,v 1.17 2004/09/26 07:29:56 gregkh Exp $ *//* FIXME: cloned devices as a use for kobjects? */ #include <linux/kernel.h> /* printk() */#include <linux/module.h>#include <linux/slab.h>   /* kmalloc() */#include <linux/fs.h>     /* everything... */#include <linux/errno.h>  /* error codes */#include <linux/types.h>  /* size_t */#include <linux/fcntl.h>#include <linux/cdev.h>#include <linux/tty.h>#include <asm/atomic.h>#include <linux/list.h>#include "scull.h"        /* local definitions */static dev_t scull_a_firstdev;  /* Where our range begins *//* * These devices fall back on the main scull operations. They only * differ in the implementation of open() and close() *//************************************************************************ * * The first device is the single-open one, *  it has an hw structure and an open count */static struct scull_dev scull_s_device;static atomic_t scull_s_available = ATOMIC_INIT(1);static int scull_s_open(struct inode *inode, struct file *filp){	struct scull_dev *dev = &scull_s_device; /* device information */	if (! atomic_dec_and_test (&scull_s_available)) {		atomic_inc(&scull_s_available);		return -EBUSY; /* already open */	}	/* then, everything else is copied from the bare scull device */	if ( (filp->f_flags & O_ACCMODE) == O_WRONLY)		scull_trim(dev);	filp->private_data = dev;	return 0;          /* success */}static int scull_s_release(struct inode *inode, struct file *filp){	atomic_inc(&scull_s_available); /* release the device */	return 0;}/* * The other operations for the single-open device come from the bare device */struct file_operations scull_sngl_fops = {	.owner =	THIS_MODULE,	.llseek =     	scull_llseek,	.read =       	scull_read,	.write =      	scull_write,	.ioctl =      	scull_ioctl,	.open =       	scull_s_open,	.release =    	scull_s_release,};/************************************************************************ * * Next, the "uid" device. It can be opened multiple times by the * same user, but access is denied to other users if the device is open */static struct scull_dev scull_u_device;static int scull_u_count;	/* initialized to 0 by default */static uid_t scull_u_owner;	/* initialized to 0 by default */static spinlock_t scull_u_lock = SPIN_LOCK_UNLOCKED;static int scull_u_open(struct inode *inode, struct file *filp){	struct scull_dev *dev = &scull_u_device; /* device information */	spin_lock(&scull_u_lock);	if (scull_u_count && 			(scull_u_owner != current->uid) &&  /* allow user */			(scull_u_owner != current->euid) && /* allow whoever did su */			!capable(CAP_DAC_OVERRIDE)) { /* still allow root */		spin_unlock(&scull_u_lock);		return -EBUSY;   /* -EPERM would confuse the user */	}	if (scull_u_count == 0)		scull_u_owner = current->uid; /* grab it */	scull_u_count++;	spin_unlock(&scull_u_lock);/* then, everything else is copied from the bare scull device */	if ((filp->f_flags & O_ACCMODE) == O_WRONLY)		scull_trim(dev);	filp->private_data = dev;	return 0;          /* success */}static int scull_u_release(struct inode *inode, struct file *filp){	spin_lock(&scull_u_lock);	scull_u_count--; /* nothing else */	spin_unlock(&scull_u_lock);	return 0;}/* * The other operations for the device come from the bare device */struct file_operations scull_user_fops = {	.owner =      THIS_MODULE,	.llseek =     scull_llseek,	.read =       scull_read,	.write =      scull_write,	.ioctl =      scull_ioctl,	.open =       scull_u_open,	.release =    scull_u_release,};/************************************************************************ * * Next, the device with blocking-open based on uid */static struct scull_dev scull_w_device;static int scull_w_count;	/* initialized to 0 by default */static uid_t scull_w_owner;	/* initialized to 0 by default */static DECLARE_WAIT_QUEUE_HEAD(scull_w_wait);static spinlock_t scull_w_lock = SPIN_LOCK_UNLOCKED;static inline int scull_w_available(void){	return scull_w_count == 0 ||		scull_w_owner == current->uid ||		scull_w_owner == current->euid ||		capable(CAP_DAC_OVERRIDE);}static int scull_w_open(struct inode *inode, struct file *filp){	struct scull_dev *dev = &scull_w_device; /* device information */	spin_lock(&scull_w_lock);	while (! scull_w_available()) {		spin_unlock(&scull_w_lock);		if (filp->f_flags & O_NONBLOCK) return -EAGAIN;		if (wait_event_interruptible (scull_w_wait, scull_w_available()))			return -ERESTARTSYS; /* tell the fs layer to handle it */		spin_lock(&scull_w_lock);	}	if (scull_w_count == 0)		scull_w_owner = current->uid; /* grab it */	scull_w_count++;	spin_unlock(&scull_w_lock);	/* then, everything else is copied from the bare scull device */	if ((filp->f_flags & O_ACCMODE) == O_WRONLY)		scull_trim(dev);	filp->private_data = dev;	return 0;          /* success */}static int scull_w_release(struct inode *inode, struct file *filp){	int temp;	spin_lock(&scull_w_lock);	scull_w_count--;	temp = scull_w_count;	spin_unlock(&scull_w_lock);	if (temp == 0)		wake_up_interruptible_sync(&scull_w_wait); /* awake other uid's */	return 0;}/* * The other operations for the device come from the bare device */struct file_operations scull_wusr_fops = {	.owner =      THIS_MODULE,	.llseek =     scull_llseek,	.read =       scull_read,	.write =      scull_write,	.ioctl =      scull_ioctl,	.open =       scull_w_open,	.release =    scull_w_release,};/************************************************************************ * * Finally the `cloned' private device. This is trickier because it * involves list management, and dynamic allocation. *//* The clone-specific data structure includes a key field */struct scull_listitem {	struct scull_dev device;	dev_t key;	struct list_head list;    };/* The list of devices, and a lock to protect it */static LIST_HEAD(scull_c_list);static spinlock_t scull_c_lock = SPIN_LOCK_UNLOCKED;/* A placeholder scull_dev which really just holds the cdev stuff. */static struct scull_dev scull_c_device;   /* Look for a device or create one if missing */static struct scull_dev *scull_c_lookfor_device(dev_t key){	struct scull_listitem *lptr;	list_for_each_entry(lptr, &scull_c_list, list) {		if (lptr->key == key)			return &(lptr->device);	}	/* not found */	lptr = kmalloc(sizeof(struct scull_listitem), GFP_KERNEL);	if (!lptr)		return NULL;	/* initialize the device */	memset(lptr, 0, sizeof(struct scull_listitem));	lptr->key = key;	scull_trim(&(lptr->device)); /* initialize it */	init_MUTEX(&(lptr->device.sem));	/* place it in the list */	list_add(&lptr->list, &scull_c_list);	return &(lptr->device);}static int scull_c_open(struct inode *inode, struct file *filp){	struct scull_dev *dev;	dev_t key; 	if (!current->signal->tty) { 		PDEBUG("Process \"%s\" has no ctl tty\n", current->comm);		return -EINVAL;	}	key = tty_devnum(current->signal->tty);	/* look for a scullc device in the list */	spin_lock(&scull_c_lock);	dev = scull_c_lookfor_device(key);	spin_unlock(&scull_c_lock);	if (!dev)		return -ENOMEM;	/* then, everything else is copied from the bare scull device */	if ( (filp->f_flags & O_ACCMODE) == O_WRONLY)		scull_trim(dev);	filp->private_data = dev;	return 0;          /* success */}static int scull_c_release(struct inode *inode, struct file *filp){	/*	 * Nothing to do, because the device is persistent.	 * A `real' cloned device should be freed on last close	 */	return 0;}/* * The other operations for the device come from the bare device */struct file_operations scull_priv_fops = {	.owner =    THIS_MODULE,	.llseek =   scull_llseek,	.read =     scull_read,	.write =    scull_write,	.ioctl =    scull_ioctl,	.open =     scull_c_open,	.release =  scull_c_release,};/************************************************************************ * * And the init and cleanup functions come last */static struct scull_adev_info {	char *name;	struct scull_dev *sculldev;	struct file_operations *fops;} scull_access_devs[] = {	{ "scullsingle", &scull_s_device, &scull_sngl_fops },	{ "sculluid", &scull_u_device, &scull_user_fops },	{ "scullwuid", &scull_w_device, &scull_wusr_fops },	{ "sullpriv", &scull_c_device, &scull_priv_fops }};#define SCULL_N_ADEVS 4/* * Set up a single device. */static void scull_access_setup (dev_t devno, struct scull_adev_info *devinfo){	struct scull_dev *dev = devinfo->sculldev;	int err;	/* Initialize the device structure */	dev->quantum = scull_quantum;	dev->qset = scull_qset;	init_MUTEX(&dev->sem);	/* Do the cdev stuff. */	cdev_init(&dev->cdev, devinfo->fops);	kobject_set_name(&dev->cdev.kobj, devinfo->name);	dev->cdev.owner = THIS_MODULE;	err = cdev_add (&dev->cdev, devno, 1);        /* Fail gracefully if need be */	if (err) {		printk(KERN_NOTICE "Error %d adding %s\n", err, devinfo->name);		kobject_put(&dev->cdev.kobj);	} else		printk(KERN_NOTICE "%s registered at %x\n", devinfo->name, devno);}int scull_access_init(dev_t firstdev){	int result, i;	/* Get our number space */	result = register_chrdev_region (firstdev, SCULL_N_ADEVS, "sculla");	if (result < 0) {		printk(KERN_WARNING "sculla: device number registration failed\n");		return 0;	}	scull_a_firstdev = firstdev;	/* Set up each device. */	for (i = 0; i < SCULL_N_ADEVS; i++)		scull_access_setup (firstdev + i, scull_access_devs + i);	return SCULL_N_ADEVS;}/* * This is called by cleanup_module or on failure. * It is required to never fail, even if nothing was initialized first */void scull_access_cleanup(void){	struct scull_listitem *lptr, *next;	int i;	/* Clean up the static devs */	for (i = 0; i < SCULL_N_ADEVS; i++) {		struct scull_dev *dev = scull_access_devs[i].sculldev;		cdev_del(&dev->cdev);		scull_trim(scull_access_devs[i].sculldev);	}    	/* And all the cloned devices */	list_for_each_entry_safe(lptr, next, &scull_c_list, list) {		list_del(&lptr->list);		scull_trim(&(lptr->device));		kfree(lptr);	}	/* Free up our number space */	unregister_chrdev_region(scull_a_firstdev, SCULL_N_ADEVS);	return;}