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    Subject[PATCH 5.19 1111/1157] dm: fix dm-raid crash if md_handle_request() splits bio
    Date
    From: Mike Snitzer <snitzer@kernel.org>

    [ Upstream commit 9dd1cd3220eca534f2d47afad7ce85f4c40118d8 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/md/dm-raid.c | 1 +
    drivers/md/dm.c | 13 ++++++-------
    include/linux/device-mapper.h | 6 ++++++
    include/uapi/linux/dm-ioctl.h | 4 ++--
    4 files changed, 15 insertions(+), 9 deletions(-)

    diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
    index a55fc28d2a29..ba3638d1d046 100644
    --- a/drivers/md/dm-raid.c
    +++ b/drivers/md/dm-raid.c
    @@ -3097,6 +3097,7 @@ 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 2b75f1ef7386..36c704b50ac3 100644
    --- a/drivers/md/dm.c
    +++ b/drivers/md/dm.c
    @@ -578,9 +578,6 @@ 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);
    @@ -614,6 +611,7 @@ 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;

    @@ -623,14 +621,10 @@ 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;
    @@ -646,6 +640,11 @@ 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 47a01c7cffdf..e9c043f12e53 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);
    diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
    index 2e9550fef90f..27ad9671f2df 100644
    --- 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 */
    --
    2.35.1


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