Re: [PATCH v6 0/3] md/raid10: fix r10bio width mismatches across reshape

[yu kuai]

Hi,

在 2026/7/11 18:03, Chen Cheng 写道:
> From: Chen Cheng <chencheng@xxxxxxxxx>
>
> Hi,
>
> This series fixes slab out-of-bounds accesses in raid10 when reshape changes
> the number of raid disks while regular I/O is still reusing r10bio objects
> allocated under the previous geometry.
>
> The bug is reproducible with a simple 4-disk to 5-disk reshape under write
> load, for example:
>
>    mdadm -C /dev/md777 -l10 -n4 /dev/sda /dev/sdb /dev/sdc /dev/sdd
>    mkfs.ext4 /dev/md777
>    mount /dev/md777 /mnt/test
>    fsstress -d /mnt/test -n 24000 -p 8 -l 24 &
>    mdadm /dev/md777 --add /dev/sde
>    mdadm --grow /dev/md777 --raid-devices=5 \
>      --backup-file=/tmp/md-reshape-backup
>
>
> KASAN report:
>
>    BUG: KASAN: slab-out-of-bounds in free_r10bio+0x1c4/0x260 [raid10]
>    Read of size 8 at addr ffff00008c2dfac8 by task ksoftirqd/0/15
>    free_r10bio
>    raid_end_bio_io
>    one_write_done
>    raid10_end_write_request
>
>
> This series addresses the problem in three steps:
>
>    1. ensure the sync_action=reshape caller suspends and locks before start_reshape
>
>    2. resize r10bio_pool when reshape grows raid_disks
>
>    3. reorder the r10bio free flow before bio_endio in the regular and discard
>       completion paths
>
> Changes in v7:
>     - patch #1, refactor out suspend from retry block
>     - patch #3, raid_end_bio_io() refactor to:
>          free(r10_bio) -> free(master_bio) -> allow_barrier
>
> Changes in v6:
>     - suspend the array in action_store() after flush_work()
>     - free r10bio before ending the discard master bio
>
> Changes in v5 (suggested by Yu Kuai):
>     - simplify patch 2
>     - switch patch 3 from bounding reused r10bio devs[] walks by used_nr_devs
>       to reordering the free/endio flow
>
> Changes in v4:
>     - make the sync_action=reshape path invoke mddev_suspend_and_lock() before
>       calling start_reshape()
>     - leave the md-cluster and dm-raid paths unchanged; they still reach
>       start_reshape() with the mddev locked but without suspend
>
> Changes in v3:
>     - replace freeze_array()/unfreeze_array() in raid10_start_reshape() with
>       mddev_suspend_and_lock_nointr()/mddev_unlock_and_resume(); freeze_array()
>       can return while retry-list items still hold pool objects, while
>       mddev_suspend() provides the correct upper-layer quiesce interface
>
> Changes in v2:
>    - add this cover letter
>    - convert r10bio_pool to a fixed-size kmalloc mempool
>    - rebuild r10bio_pool inside the freeze window before switching live reshape
>      geometry
>    - switch raid10_quiesce() to freeze_array()/unfreeze_array()
>
>
> Testing:
>    - reproduced the original KASAN slab-out-of-bounds on 4-disk -> 5-disk
>      raid10 reshape with fsstress
>    - verified that this series fixes that reproducer
>    - exercised the 5-disk -> 4-disk reshape direction as well
>
> Thanks,
> Chen Cheng
>
>
>
> Chen Cheng (3):
>    md: suspend array when sync_action=reshape
>    md/raid10: resize r10bio_pool for reshape
>    md/raid10: free r10bio before ending master_bio in raid_end_bio_io()
>      and raid_end_discard_bio()
>
>   drivers/md/md.c     | 17 +++++++++----
>   drivers/md/raid10.c | 61 ++++++++++++++++++++++++++++++++-------------
>   drivers/md/raid10.h |  2 +-
>   3 files changed, 56 insertions(+), 24 deletions(-)

Applied to md-7.3 with a few changes, please check the latest md-7.3 branch:

   - Patch 2: removed the redundant if (new_pool) before mempool_destroy(new_pool) to fix the
     strict checkpatch warning.

   - Patch 3: rewrote raid_end_bio_io() minimally so the existing R10BIO_* bit-test lines stay in
     place and checkpatch no longer flags CamelCase additions. This also preserves setting
     R10BIO_Returned in r10_bio->state before freeing.

   - Patch 3 commit message: corrected the listed final order to free_r10bio() -> bio_endio() ->
     allow_barrier().

>
-- 
Thanks,
Kuai