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 <snitzer@kernel.org>

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index e6a9b8c..3203aec 100644 (file)
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -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);

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 47bcc50..f6a6437 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -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))

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 920085d..04c6acf 100644 (file)
--- 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);

diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index 2e9550f..27ad967 100644 (file)
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -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 */