From 9dd1cd3220eca534f2d47afad7ce85f4c40118d8 Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Wed, 20 Jul 2022 13:58:04 -0400 Subject: dm: fix dm-raid crash if md_handle_request() splits bio Commit ca522482e3eaf ("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: ca522482e3eaf ("dm: pass NULL bdev to bio_alloc_clone") Cc: stable@vger.kernel.org Signed-off-by: Mike Snitzer --- include/linux/device-mapper.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include/linux') diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h index 920085dd7f3b..04c6acf7faaa 100644 --- a/include/linux/device-mapper.h +++ b/include/linux/device-mapper.h @@ -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); -- cgit v1.2.3