Commit 6d69bb53 authored by Ilya Dryomov's avatar Ilya Dryomov
Browse files

rbd: prevent kernel stack blow up on rbd map 

Mapping an image with a long parent chain (e.g. image foo, whose parent
is bar, whose parent is baz, etc) currently leads to a kernel stack
overflow, due to the following recursion in the reply path:

  rbd_osd_req_callback()
    rbd_obj_request_complete()
      rbd_img_obj_callback()
        rbd_img_parent_read_callback()
          rbd_obj_request_complete()
            ...

Limit the parent chain to 16 images, which is ~5K worth of stack.  When
the above recursion is eliminated, this limit can be lifted.

Fixes: http://tracker.ceph.com/issues/12538



Cc: stable@vger.kernel.org # 3.10+, needs backporting for < 4.2
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
Reviewed-by: default avatarJosh Durgin <jdurgin@redhat.com>
parent 1f2c6651

drivers/block/rbd.c

+23 −10
Original line number Diff line number Diff line
@@ -96,6 +96,8 @@ static int atomic_dec_return_safe(atomic_t *v) 
#define RBD_MINORS_PER_MAJOR		256

#define RBD_SINGLE_MAJOR_PART_SHIFT	4



#define RBD_MAX_PARENT_CHAIN_LEN	16



#define RBD_SNAP_DEV_NAME_PREFIX	"snap_"

#define RBD_MAX_SNAP_NAME_LEN	\

			(NAME_MAX - (sizeof (RBD_SNAP_DEV_NAME_PREFIX) - 1))
@@ -426,7 +428,7 @@ static ssize_t rbd_add_single_major(struct bus_type *bus, const char *buf, 
				    size_t count);

static ssize_t rbd_remove_single_major(struct bus_type *bus, const char *buf,

				       size_t count);

static int rbd_dev_image_probe(struct rbd_device *rbd_dev, bool mapping);

static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth);

static void rbd_spec_put(struct rbd_spec *spec);



static int rbd_dev_id_to_minor(int dev_id)
@@ -5131,7 +5133,12 @@ out_err: 
	return ret;

}



static int rbd_dev_probe_parent(struct rbd_device *rbd_dev)

/*

 * @depth is rbd_dev_image_probe() -> rbd_dev_probe_parent() ->

 * rbd_dev_image_probe() recursion depth, which means it's also the

 * length of the already discovered part of the parent chain.

 */

static int rbd_dev_probe_parent(struct rbd_device *rbd_dev, int depth)

{

	struct rbd_device *parent = NULL;

	int ret;
@@ -5139,6 +5146,12 @@ static int rbd_dev_probe_parent(struct rbd_device *rbd_dev) 
	if (!rbd_dev->parent_spec)

		return 0;



	if (++depth > RBD_MAX_PARENT_CHAIN_LEN) {

		pr_info("parent chain is too long (%d)\n", depth);

		ret = -EINVAL;

		goto out_err;

	}



	parent = rbd_dev_create(rbd_dev->rbd_client, rbd_dev->parent_spec,

				NULL);

	if (!parent) {
@@ -5153,7 +5166,7 @@ static int rbd_dev_probe_parent(struct rbd_device *rbd_dev) 
	__rbd_get_client(rbd_dev->rbd_client);

	rbd_spec_get(rbd_dev->parent_spec);



	ret = rbd_dev_image_probe(parent, false);

	ret = rbd_dev_image_probe(parent, depth);

	if (ret < 0)

		goto out_err;
@@ -5282,7 +5295,7 @@ static void rbd_dev_image_release(struct rbd_device *rbd_dev) 
 * parent), initiate a watch on its header object before using that

 * object to get detailed information about the rbd image.

 */

static int rbd_dev_image_probe(struct rbd_device *rbd_dev, bool mapping)

static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)

{

	int ret;
@@ -5300,7 +5313,7 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, bool mapping) 
	if (ret)

		goto err_out_format;



	if (mapping) {

	if (!depth) {

		ret = rbd_dev_header_watch_sync(rbd_dev);

		if (ret) {

			if (ret == -ENOENT)
@@ -5321,7 +5334,7 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, bool mapping) 
	 * Otherwise this is a parent image, identified by pool, image

	 * and snap ids - need to fill in names for those ids.

	 */

	if (mapping)

	if (!depth)

		ret = rbd_spec_fill_snap_id(rbd_dev);

	else

		ret = rbd_spec_fill_names(rbd_dev);
@@ -5343,12 +5356,12 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, bool mapping) 
		 * Need to warn users if this image is the one being

		 * mapped and has a parent.

		 */

		if (mapping && rbd_dev->parent_spec)

		if (!depth && rbd_dev->parent_spec)

			rbd_warn(rbd_dev,

				 "WARNING: kernel layering is EXPERIMENTAL!");

	}



	ret = rbd_dev_probe_parent(rbd_dev);

	ret = rbd_dev_probe_parent(rbd_dev, depth);

	if (ret)

		goto err_out_probe;
@@ -5359,7 +5372,7 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, bool mapping) 
err_out_probe:

	rbd_dev_unprobe(rbd_dev);

err_out_watch:

	if (mapping)

	if (!depth)

		rbd_dev_header_unwatch_sync(rbd_dev);

out_header_name:

	kfree(rbd_dev->header_name);
@@ -5422,7 +5435,7 @@ static ssize_t do_rbd_add(struct bus_type *bus, 
	spec = NULL;		/* rbd_dev now owns this */

	rbd_opts = NULL;	/* rbd_dev now owns this */



	rc = rbd_dev_image_probe(rbd_dev, true);

	rc = rbd_dev_image_probe(rbd_dev, 0);

	if (rc < 0)

		goto err_out_rbd_dev;

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