CVE-2024-26757

In the Linux kernel, the following vulnerability has been resolved: md:
Don’t ignore read-only array in md_check_recovery() Usually if the array is
not read-write, md_check_recovery() won’t register new sync_thread in the
first place. And if the array is read-write and sync_thread is registered,
md_set_readonly() will unregister sync_thread before setting the array
read-only. md/raid follow this behavior hence there is no problem. After
commit f52f5c71f3d4 (“md: fix stopping sync thread”), following hang can be
triggered by test shell/integrity-caching.sh: 1) array is read-only.
dm-raid update super block: rs_update_sbs ro = mddev->ro mddev->ro = 0 ->
set array read-write md_update_sb 2) register new sync thread concurrently.
3) dm-raid set array back to read-only: rs_update_sbs mddev->ro = ro 4)
stop the array: raid_dtr md_stop stop_sync_thread set_bit(MD_RECOVERY_INTR,
&mddev->recovery); md_wakeup_thread_directly(mddev->sync_thread);
wait_event(…, !test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) 5) sync
thread done: md_do_sync set_bit(MD_RECOVERY_DONE, &mddev->recovery);
md_wakeup_thread(mddev->thread); 6) daemon thread can’t unregister sync
thread: md_check_recovery if (!md_is_rdwr(mddev) &&
!test_bit(MD_RECOVERY_NEEDED, &mddev->recovery)) return; -> ->
MD_RECOVERY_RUNNING can’t be cleared, hence step 4 hang; The root cause is
that dm-raid manipulate ‘mddev->ro’ by itself, however, dm-raid really
should stop sync thread before setting the array read-only. Unfortunately,
I need to read more code before I can refacter the handler of ‘mddev->ro’
in dm-raid, hence let’s fix the problem the easy way for now to prevent
dm-raid regression.