Commit message: staging/android/ion : fix a race condition in the ion driver

There is a use-after-free problem in the ion driver.
This is caused by a race condition in the ion_ioctl()
function.

A handle has ref count of 1 and two tasks on different
cpus calls ION_IOC_FREE simultaneously.

cpu 0                                   cpu 1
-------------------------------------------------------
ion_handle_get_by_id()
(ref == 2)
                            ion_handle_get_by_id()
                            (ref == 3)

ion_free()
(ref == 2)

ion_handle_put()
(ref == 1)

                            ion_free()
                            (ref == 0 so ion_handle_destroy() is
                            called
                            and the handle is freed.)

                            ion_handle_put() is called and it
                            decreases the slub's next free pointer

The problem is detected as an unaligned access in the
spin lock functions since it uses load exclusive
 instruction. In some cases it corrupts the slub's
free pointer which causes a mis-aligned access to the
next free pointer.(kmalloc returns a pointer like
ffffc0745b4580aa). And it causes lots of other
hard-to-debug problems.

This symptom is caused since the first member in the
ion_handle structure is the reference count and the
ion driver decrements the reference after it has been
freed.

To fix this problem client->lock mutex is extended
to protect all the codes that uses the handle.

Signed-off-by: Eun Taik Lee <eun.taik.lee@samsung.com>
Reviewed-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CVE: CVE-2016-9120
CWE: CWE-416
Vulnerability description: Race condition in the ion_ioctl function in drivers/staging/android/ion/ion.c in the Linux kernel before 4.6 allows local users to gain privileges or cause a denial of service (use-after-free) by calling ION_IOC_FREE on two CPUs at the same time.

Project: linux

struct ion_handle *ion_alloc(struct ion_client *client, size_t len,
			     size_t align, unsigned int heap_id_mask,
			     unsigned int flags)
{
	struct ion_handle *handle;
	struct ion_device *dev = client->dev;
	struct ion_buffer *buffer = NULL;
	struct ion_heap *heap;
	int ret;

	pr_debug("%s: len %zu align %zu heap_id_mask %u flags %x\n", __func__,
		 len, align, heap_id_mask, flags);
	/*
	 * traverse the list of heaps available in this system in priority
	 * order.  If the heap type is supported by the client, and matches the
	 * request of the caller allocate from it.  Repeat until allocate has
	 * succeeded or all heaps have been tried
	 */
	len = PAGE_ALIGN(len);

	if (!len)
		return ERR_PTR(-EINVAL);

	down_read(&dev->lock);
	plist_for_each_entry(heap, &dev->heaps, node) {
		/* if the caller didn't specify this heap id */
		if (!((1 << heap->id) & heap_id_mask))
			continue;
		buffer = ion_buffer_create(heap, dev, len, align, flags);
		if (!IS_ERR(buffer))
			break;
	}
	up_read(&dev->lock);

	if (buffer == NULL)
		return ERR_PTR(-ENODEV);

	if (IS_ERR(buffer))
		return ERR_CAST(buffer);

	handle = ion_handle_create(client, buffer);

	/*
	 * ion_buffer_create will create a buffer with a ref_cnt of 1,
	 * and ion_handle_create will take a second reference, drop one here
	 */
	ion_buffer_put(buffer);

	if (IS_ERR(handle))
		return handle;

	mutex_lock(&client->lock);
	ret = ion_handle_add(client, handle);
	mutex_unlock(&client->lock);
	if (ret) {
		ion_handle_put(handle);
		handle = ERR_PTR(ret);
	}

	return handle;
 }

Project: linux

static inline bool ion_buffer_page_is_dirty(struct page *page)
{
	return !!((unsigned long)page & 1UL);
}

Project: linux

static int ion_buffer_put(struct ion_buffer *buffer)
{
	return kref_put(&buffer->ref, _ion_buffer_destroy);
}

Project: linux

struct ion_client *ion_client_create(struct ion_device *dev,
				     const char *name)
{
	struct ion_client *client;
	struct task_struct *task;
	struct rb_node **p;
	struct rb_node *parent = NULL;
	struct ion_client *entry;
	pid_t pid;

	if (!name) {
		pr_err("%s: Name cannot be null\n", __func__);
		return ERR_PTR(-EINVAL);
	}

	get_task_struct(current->group_leader);
	task_lock(current->group_leader);
	pid = task_pid_nr(current->group_leader);
	/*
	 * don't bother to store task struct for kernel threads,
	 * they can't be killed anyway
	 */
	if (current->group_leader->flags & PF_KTHREAD) {
		put_task_struct(current->group_leader);
		task = NULL;
	} else {
		task = current->group_leader;
	}
	task_unlock(current->group_leader);

	client = kzalloc(sizeof(struct ion_client), GFP_KERNEL);
	if (!client)
		goto err_put_task_struct;

	client->dev = dev;
	client->handles = RB_ROOT;
	idr_init(&client->idr);
	mutex_init(&client->lock);
	client->task = task;
	client->pid = pid;
	client->name = kstrdup(name, GFP_KERNEL);
	if (!client->name)
		goto err_free_client;

	down_write(&dev->lock);
	client->display_serial = ion_get_client_serial(&dev->clients, name);
	client->display_name = kasprintf(
		GFP_KERNEL, "%s-%d", name, client->display_serial);
	if (!client->display_name) {
		up_write(&dev->lock);
		goto err_free_client_name;
	}
	p = &dev->clients.rb_node;
	while (*p) {
		parent = *p;
		entry = rb_entry(parent, struct ion_client, node);

		if (client < entry)
			p = &(*p)->rb_left;
		else if (client > entry)
			p = &(*p)->rb_right;
	}
	rb_link_node(&client->node, parent, p);
	rb_insert_color(&client->node, &dev->clients);

	client->debug_root = debugfs_create_file(client->display_name, 0664,
						dev->clients_debug_root,
						client, &debug_client_fops);
	if (!client->debug_root) {
		char buf[256], *path;

		path = dentry_path(dev->clients_debug_root, buf, 256);
		pr_err("Failed to create client debugfs at %s/%s\n",
			path, client->display_name);
	}

	up_write(&dev->lock);

	return client;

err_free_client_name:
	kfree(client->name);
err_free_client:
	kfree(client);
err_put_task_struct:
	if (task)
		put_task_struct(current->group_leader);
	return ERR_PTR(-ENOMEM);
}

Project: linux

static int ion_debug_client_open(struct inode *inode, struct file *file)
{
	return single_open(file, ion_debug_client_show, inode->i_private);
}

Project: linux

static int ion_debug_client_show(struct seq_file *s, void *unused)
{
	struct ion_client *client = s->private;
	struct rb_node *n;
	size_t sizes[ION_NUM_HEAP_IDS] = {0};
	const char *names[ION_NUM_HEAP_IDS] = {NULL};
	int i;

	mutex_lock(&debugfs_mutex);
	if (!is_client_alive(client)) {
		seq_printf(s, "ion_client 0x%p dead, can't dump its buffers\n",
			   client);
		mutex_unlock(&debugfs_mutex);
		return 0;
	}

	mutex_lock(&client->lock);
	for (n = rb_first(&client->handles); n; n = rb_next(n)) {
		struct ion_handle *handle = rb_entry(n, struct ion_handle,
						     node);
		unsigned int id = handle->buffer->heap->id;

		if (!names[id])
			names[id] = handle->buffer->heap->name;
		sizes[id] += handle->buffer->size;
	}
	mutex_unlock(&client->lock);
	mutex_unlock(&debugfs_mutex);

	seq_printf(s, "%16.16s: %16.16s\n", "heap_name", "size_in_bytes");
	for (i = 0; i < ION_NUM_HEAP_IDS; i++) {
		if (!names[i])
			continue;
		seq_printf(s, "%16.16s: %16zu\n", names[i], sizes[i]);
	}
	return 0;
}

Project: linux

void ion_unmap_kernel(struct ion_client *client, struct ion_handle *handle)
{
	struct ion_buffer *buffer;

	mutex_lock(&client->lock);
	buffer = handle->buffer;
	mutex_lock(&buffer->lock);
	ion_handle_kmap_put(handle);
	mutex_unlock(&buffer->lock);
	mutex_unlock(&client->lock);
}