md/raid5: reject zero-sector reshape chunks

Browse source

Sashiko reported that RAID5 can accept a reshape chunk size that becomes
zero sectors. chunk_size_store() stores the sysfs byte value as n >> 9, so
writing a value below 512 bytes sets mddev->new_chunk_sectors to zero.
RAID5 then accepted that pending reshape geometry and raid5_start_reshape()
installed it into conf->chunk_sectors, letting reshape code divide by zero.

Reject zero-sector chunks both in check_reshape(), where normal sysfs
requests are validated, and in raid5_start_reshape(), so assembly/resume
paths also cannot install zero chunk geometry.

Test script: in QEMU, create a plain three-disk RAID5 array with 64K
chunks, write/read back a small pattern, write 1 to
/sys/block/md0/md/chunk_size, add a fourth disk, and run mdadm --grow
--raid-devices=4 --backup-file=... . The script scans dmesg for divide
error/Oops/KASAN signatures.

Bad kernel, eb29914412c3:

  echo 1 > /sys/block/md0/md/chunk_size
  mdadm --grow /dev/md0 --raid-devices=4 --backup-file=/root/md0-grow.bak

  Oops: divide error: 0000 [#1] SMP KASAN NOPTI
  RIP: raid5_get_active_stripe+0x863/0xc10
  Call Trace:
   raid5_sync_request
   md_do_sync
   md_thread
  Kernel panic - not syncing: Fatal exception

Fixed kernel: echo 1 > /sys/block/md0/md/chunk_size bash: echo: write
error: Invalid argument chunk_write_rc=1 grow_rc=skipped RESULT:
REJECTED_ZERO_CHUNK_NO_OOPS

Tested-by: Mykola Marzhan <mykola@meshstor.io>
Link: https://patch.msgid.link/20260802195038.164272-5-yukuai@kernel.org
Signed-off-by: Yu Kuai <yukuai@fygo.io>

...

This commit is contained in:

Yu Kuai 2026-08-03 03:50:13 +08:00

parent dbd21b489a

commit a41bb2ee1a

1 changed files with 5 additions and 0 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

5

drivers/md/raid5.c

View file