From 6d69bb536bac0d403d83db1ca841444981b280cd Mon Sep 17 00:00:00 2001 From: Ilya Dryomov Date: Sun, 11 Oct 2015 19:38:00 +0200 Subject: [PATCH] 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: Ilya Dryomov Reviewed-by: Josh Durgin --- drivers/block/rbd.c | 33 +++++++++++++++++++++++---------- 1 file changed, 23 insertions(+), 10 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 028db28..6f26cf3 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -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; -- 2.7.4