Commit message: cuse: fix memory leak

The problem is that fuse_dev_alloc() acquires an extra reference to cc.fc,
and the original ref count is never dropped.

Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Fixes: cc080e9e9be1 ("fuse: introduce per-instance fuse_dev structure")
Cc: <stable@vger.kernel.org> # v4.2+
CVE: CVE-2015-1339
CWE: CWE-399
Vulnerability description: Memory leak in the cuse_channel_release function in fs/fuse/cuse.c in the Linux kernel before 4.4 allows local users to cause a denial of service (memory consumption) or possibly have unspecified other impact by opening /dev/cuse many times.

Project: linux

static int cuse_channel_open(struct inode *inode, struct file *file)
{
	struct fuse_dev *fud;
	struct cuse_conn *cc;
	int rc;

	/* set up cuse_conn */
	cc = kzalloc(sizeof(*cc), GFP_KERNEL);
	if (!cc)
		return -ENOMEM;

	fuse_conn_init(&cc->fc);

	fud = fuse_dev_alloc(&cc->fc);
	if (!fud) {
		kfree(cc);
		return -ENOMEM;
	}

	INIT_LIST_HEAD(&cc->list);
	cc->fc.release = cuse_fc_release;

	cc->fc.initialized = 1;
	rc = cuse_send_init(cc);
	if (rc) {
		fuse_dev_free(fud);
		return rc;
	}
	file->private_data = fud;

	return 0;
}

Project: linux

static ssize_t cuse_class_abort_store(struct device *dev,
				      struct device_attribute *attr,
				      const char *buf, size_t count)
{
	struct cuse_conn *cc = dev_get_drvdata(dev);

	fuse_abort_conn(&cc->fc);
	return count;
}

Project: linux

static ssize_t cuse_class_waiting_show(struct device *dev,
				       struct device_attribute *attr, char *buf)
{
	struct cuse_conn *cc = dev_get_drvdata(dev);

	return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
}

Project: linux

static struct list_head *cuse_conntbl_head(dev_t devt)
{
	return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
}

Project: linux

static void __exit cuse_exit(void)
{
	misc_deregister(&cuse_miscdev);
	class_destroy(cuse_class);
}

Project: linux

static void cuse_fc_release(struct fuse_conn *fc)
{
	struct cuse_conn *cc = fc_to_cc(fc);
	kfree_rcu(cc, fc.rcu);
}

Project: linux

static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
				   unsigned long arg)
{
	struct fuse_file *ff = file->private_data;
	struct cuse_conn *cc = fc_to_cc(ff->fc);
	unsigned int flags = FUSE_IOCTL_COMPAT;

	if (cc->unrestricted_ioctl)
		flags |= FUSE_IOCTL_UNRESTRICTED;

	return fuse_do_ioctl(file, cmd, arg, flags);
}

Project: linux

static long cuse_file_ioctl(struct file *file, unsigned int cmd,
			    unsigned long arg)
{
	struct fuse_file *ff = file->private_data;
	struct cuse_conn *cc = fc_to_cc(ff->fc);
	unsigned int flags = 0;

	if (cc->unrestricted_ioctl)
		flags |= FUSE_IOCTL_UNRESTRICTED;

	return fuse_do_ioctl(file, cmd, arg, flags);
}

Project: linux

static void cuse_gendev_release(struct device *dev)
{
	kfree(dev);
}

Project: linux

static int __init cuse_init(void)
{
	int i, rc;

	/* init conntbl */
	for (i = 0; i < CUSE_CONNTBL_LEN; i++)
		INIT_LIST_HEAD(&cuse_conntbl[i]);

	/* inherit and extend fuse_dev_operations */
	cuse_channel_fops		= fuse_dev_operations;
	cuse_channel_fops.owner		= THIS_MODULE;
	cuse_channel_fops.open		= cuse_channel_open;
	cuse_channel_fops.release	= cuse_channel_release;

	cuse_class = class_create(THIS_MODULE, "cuse");
	if (IS_ERR(cuse_class))
		return PTR_ERR(cuse_class);

	cuse_class->dev_groups = cuse_class_dev_groups;

	rc = misc_register(&cuse_miscdev);
	if (rc) {
		class_destroy(cuse_class);
		return rc;
	}

	return 0;
}

Project: linux

static int cuse_open(struct inode *inode, struct file *file)
{
	dev_t devt = inode->i_cdev->dev;
	struct cuse_conn *cc = NULL, *pos;
	int rc;

	/* look up and get the connection */
	mutex_lock(&cuse_lock);
	list_for_each_entry(pos, cuse_conntbl_head(devt), list)
		if (pos->dev->devt == devt) {
			fuse_conn_get(&pos->fc);
			cc = pos;
			break;
		}
	mutex_unlock(&cuse_lock);

	/* dead? */
	if (!cc)
		return -ENODEV;

	/*
	 * Generic permission check is already done against the chrdev
	 * file, proceed to open.
	 */
	rc = fuse_do_open(&cc->fc, 0, file, 0);
	if (rc)
		fuse_conn_put(&cc->fc);
	return rc;
}

Project: linux

static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
{
	char *end = p + len;
	char *uninitialized_var(key), *uninitialized_var(val);
	int rc;

	while (true) {
		rc = cuse_parse_one(&p, end, &key, &val);
		if (rc < 0)
			return rc;
		if (!rc)
			break;
		if (strcmp(key, "DEVNAME") == 0)
			devinfo->name = val;
		else
			printk(KERN_WARNING "CUSE: unknown device info \"%s\"\n",
			       key);
	}

	if (!devinfo->name || !strlen(devinfo->name)) {
		printk(KERN_ERR "CUSE: DEVNAME unspecified\n");
		return -EINVAL;
	}

	return 0;
}

Project: linux

static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
{
	char *p = *pp;
	char *key, *val;

	while (p < end && *p == '\0')
		p++;
	if (p == end)
		return 0;

	if (end[-1] != '\0') {
		printk(KERN_ERR "CUSE: info not properly terminated\n");
		return -EINVAL;
	}

	key = val = p;
	p += strlen(p);

	if (valp) {
		strsep(&val, "=");
		if (!val)
			val = key + strlen(key);
		key = strstrip(key);
		val = strstrip(val);
	} else
		key = strstrip(key);

	if (!strlen(key)) {
		printk(KERN_ERR "CUSE: zero length info key specified\n");
		return -EINVAL;
	}

	*pp = p;
	*keyp = key;
	if (valp)
		*valp = val;

	return 1;
}

Project: linux

static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
{
	struct cuse_conn *cc = fc_to_cc(fc), *pos;
	struct cuse_init_out *arg = req->out.args[0].value;
	struct page *page = req->pages[0];
	struct cuse_devinfo devinfo = { };
	struct device *dev;
	struct cdev *cdev;
	dev_t devt;
	int rc, i;

	if (req->out.h.error ||
	    arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) {
		goto err;
	}

	fc->minor = arg->minor;
	fc->max_read = max_t(unsigned, arg->max_read, 4096);
	fc->max_write = max_t(unsigned, arg->max_write, 4096);

	/* parse init reply */
	cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;

	rc = cuse_parse_devinfo(page_address(page), req->out.args[1].size,
				&devinfo);
	if (rc)
		goto err;

	/* determine and reserve devt */
	devt = MKDEV(arg->dev_major, arg->dev_minor);
	if (!MAJOR(devt))
		rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
	else
		rc = register_chrdev_region(devt, 1, devinfo.name);
	if (rc) {
		printk(KERN_ERR "CUSE: failed to register chrdev region\n");
		goto err;
	}

	/* devt determined, create device */
	rc = -ENOMEM;
	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
		goto err_region;

	device_initialize(dev);
	dev_set_uevent_suppress(dev, 1);
	dev->class = cuse_class;
	dev->devt = devt;
	dev->release = cuse_gendev_release;
	dev_set_drvdata(dev, cc);
	dev_set_name(dev, "%s", devinfo.name);

	mutex_lock(&cuse_lock);

	/* make sure the device-name is unique */
	for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
		list_for_each_entry(pos, &cuse_conntbl[i], list)
			if (!strcmp(dev_name(pos->dev), dev_name(dev)))
				goto err_unlock;
	}

	rc = device_add(dev);
	if (rc)
		goto err_unlock;

	/* register cdev */
	rc = -ENOMEM;
	cdev = cdev_alloc();
	if (!cdev)
		goto err_unlock;

	cdev->owner = THIS_MODULE;
	cdev->ops = &cuse_frontend_fops;

	rc = cdev_add(cdev, devt, 1);
	if (rc)
		goto err_cdev;

	cc->dev = dev;
	cc->cdev = cdev;

	/* make the device available */
	list_add(&cc->list, cuse_conntbl_head(devt));
	mutex_unlock(&cuse_lock);

	/* announce device availability */
	dev_set_uevent_suppress(dev, 0);
	kobject_uevent(&dev->kobj, KOBJ_ADD);
out:
	kfree(arg);
	__free_page(page);
	return;

err_cdev:
	cdev_del(cdev);
err_unlock:
	mutex_unlock(&cuse_lock);
	put_device(dev);
err_region:
	unregister_chrdev_region(devt, 1);
err:
	fuse_abort_conn(fc);
	goto out;
}

Project: linux

static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
{
	struct fuse_io_priv io = { .async = 0, .file = kiocb->ki_filp };
	loff_t pos = 0;

	return fuse_direct_io(&io, to, &pos, FUSE_DIO_CUSE);
}

Project: linux

static int cuse_release(struct inode *inode, struct file *file)
{
	struct fuse_file *ff = file->private_data;
	struct fuse_conn *fc = ff->fc;

	fuse_sync_release(ff, file->f_flags);
	fuse_conn_put(fc);

	return 0;
}

Project: linux

static int cuse_send_init(struct cuse_conn *cc)
{
	int rc;
	struct fuse_req *req;
	struct page *page;
	struct fuse_conn *fc = &cc->fc;
	struct cuse_init_in *arg;
	void *outarg;

	BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);

	req = fuse_get_req_for_background(fc, 1);
	if (IS_ERR(req)) {
		rc = PTR_ERR(req);
		goto err;
	}

	rc = -ENOMEM;
	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
	if (!page)
		goto err_put_req;

	outarg = kzalloc(sizeof(struct cuse_init_out), GFP_KERNEL);
	if (!outarg)
		goto err_free_page;

	arg = &req->misc.cuse_init_in;
	arg->major = FUSE_KERNEL_VERSION;
	arg->minor = FUSE_KERNEL_MINOR_VERSION;
	arg->flags |= CUSE_UNRESTRICTED_IOCTL;
	req->in.h.opcode = CUSE_INIT;
	req->in.numargs = 1;
	req->in.args[0].size = sizeof(struct cuse_init_in);
	req->in.args[0].value = arg;
	req->out.numargs = 2;
	req->out.args[0].size = sizeof(struct cuse_init_out);
	req->out.args[0].value = outarg;
	req->out.args[1].size = CUSE_INIT_INFO_MAX;
	req->out.argvar = 1;
	req->out.argpages = 1;
	req->pages[0] = page;
	req->page_descs[0].length = req->out.args[1].size;
	req->num_pages = 1;
	req->end = cuse_process_init_reply;
	fuse_request_send_background(fc, req);

	return 0;

err_free_page:
	__free_page(page);
err_put_req:
	fuse_put_request(fc, req);
err:
	return rc;
}

Project: linux

static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
{
	struct fuse_io_priv io = { .async = 0, .file = kiocb->ki_filp };
	loff_t pos = 0;
	/*
	 * No locking or generic_write_checks(), the server is
	 * responsible for locking and sanity checks.
	 */
	return fuse_direct_io(&io, from, &pos,
			      FUSE_DIO_WRITE | FUSE_DIO_CUSE);
}

Project: linux

static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
{
	return container_of(fc, struct cuse_conn, fc);
}