CVE-2024-26757 Information

Apr 04, 2024 cve

Description

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.

Reference

https://git.kernel.org/stable/c/2ea169c5a0b1134d573d07fc27a16f327ad0e7d3 https://git.kernel.org/stable/c/55a48ad2db64737f7ffc0407634218cc6e4c513b

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