Commit 9dd1cd32 authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm: fix dm-raid crash if md_handle_request() splits bio 



Commit ca522482 ("dm: pass NULL bdev to bio_alloc_clone")
introduced the optimization to _not_ perform bio_associate_blkg()'s
relatively costly work when DM core clones its bio. But in doing so it
exposed the possibility for DM's cloned bio to alter DM target
behavior (e.g. crash) if a target were to issue IO without first
calling bio_set_dev().

The DM raid target can trigger an MD crash due to its need to split
the DM bio that is passed to md_handle_request(). The split will
recurse to submit_bio_noacct() using a bio with an uninitialized
->bi_blkg. This NULL bio->bi_blkg causes blk_throtl_bio() to
dereference a NULL blkg_to_tg(bio->bi_blkg).

Fix this in DM core by adding a new 'needs_bio_set_dev' target flag that
will make alloc_tio() call bio_set_dev() on behalf of the target.
dm-raid is the only target that requires this flag. bio_set_dev()
initializes the DM cloned bio's ->bi_blkg, using bio_associate_blkg,
before passing the bio to md_handle_request().

Long-term fix would be to audit and refactor MD code to rely on DM to
split its bio, using dm_accept_partial_bio(), but there are MD raid
personalities (e.g. raid1 and raid10) whose implementation are tightly
coupled to handling the bio splitting inline.

Fixes: ca522482 ("dm: pass NULL bdev to bio_alloc_clone")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
parent 7dad24db

drivers/md/dm-raid.c

+1 −0
Original line number Diff line number Diff line
@@ -3095,6 +3095,7 @@ static int raid_ctr(struct dm_target *ti, unsigned int argc, char **argv) 
	INIT_WORK(&rs->md.event_work, do_table_event);

	ti->private = rs;

	ti->num_flush_bios = 1;

	ti->needs_bio_set_dev = true;



	/* Restore any requested new layout for conversion decision */

	rs_config_restore(rs, &rs_layout);

drivers/md/dm.c

+6 −7
Original line number Diff line number Diff line
@@ -574,9 +574,6 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio) 
	struct bio *clone;



	clone = bio_alloc_clone(NULL, bio, GFP_NOIO, &md->mempools->io_bs);

	/* Set default bdev, but target must bio_set_dev() before issuing IO */

	clone->bi_bdev = md->disk->part0;



	tio = clone_to_tio(clone);

	tio->flags = 0;

	dm_tio_set_flag(tio, DM_TIO_INSIDE_DM_IO);
@@ -609,6 +606,7 @@ static void free_io(struct dm_io *io) 
static struct bio *alloc_tio(struct clone_info *ci, struct dm_target *ti,

			     unsigned target_bio_nr, unsigned *len, gfp_t gfp_mask)

{

	struct mapped_device *md = ci->io->md;

	struct dm_target_io *tio;

	struct bio *clone;
@@ -618,14 +616,10 @@ static struct bio *alloc_tio(struct clone_info *ci, struct dm_target *ti, 
		/* alloc_io() already initialized embedded clone */

		clone = &tio->clone;

	} else {

		struct mapped_device *md = ci->io->md;



		clone = bio_alloc_clone(NULL, ci->bio, gfp_mask,

					&md->mempools->bs);

		if (!clone)

			return NULL;

		/* Set default bdev, but target must bio_set_dev() before issuing IO */

		clone->bi_bdev = md->disk->part0;



		/* REQ_DM_POLL_LIST shouldn't be inherited */

		clone->bi_opf &= ~REQ_DM_POLL_LIST;
@@ -641,6 +635,11 @@ static struct bio *alloc_tio(struct clone_info *ci, struct dm_target *ti, 
	tio->len_ptr = len;

	tio->old_sector = 0;



	/* Set default bdev, but target must bio_set_dev() before issuing IO */

	clone->bi_bdev = md->disk->part0;

	if (unlikely(ti->needs_bio_set_dev))

		bio_set_dev(clone, md->disk->part0);



	if (len) {

		clone->bi_iter.bi_size = to_bytes(*len);

		if (bio_integrity(clone))

include/linux/device-mapper.h

+6 −0
Original line number Diff line number Diff line
@@ -373,6 +373,12 @@ struct dm_target { 
	 * after returning DM_MAPIO_SUBMITTED from its map function.

	 */

	bool accounts_remapped_io:1;



	/*

	 * Set if the target will submit the DM bio without first calling

	 * bio_set_dev(). NOTE: ideally a target should _not_ need this.

	 */

	bool needs_bio_set_dev:1;

};



void *dm_per_bio_data(struct bio *bio, size_t data_size);

include/uapi/linux/dm-ioctl.h

+2 −2
Original line number Diff line number Diff line
@@ -286,9 +286,9 @@ enum { 
#define DM_DEV_SET_GEOMETRY	_IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)



#define DM_VERSION_MAJOR	4

#define DM_VERSION_MINOR	46

#define DM_VERSION_MINOR	47

#define DM_VERSION_PATCHLEVEL	0

#define DM_VERSION_EXTRA	"-ioctl (2022-02-22)"

#define DM_VERSION_EXTRA	"-ioctl (2022-07-28)"



/* Status bits */

#define DM_READONLY_FLAG	(1 << 0) /* In/Out */