CVE-2024-26757

In the Linux kernel, the following vulnerability has been resolved:

md: Dont ignore read-only array in md_check_recovery()

Usually if the array is not read-write, md_check_recovery() wont 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 cant unregister sync thread: md_check_recovery if (!md_is_rdwr(mddev) && !test_bit(MD_RECOVERY_NEEDED, &mddev->recovery)) return; -> -> MD_RECOVERY_RUNNING cant 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 lets fix the problem the easy way for now to prevent dm-raid regression.

Weakness

The product does not release or incorrectly releases a resource before it is made available for re-use.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, languages such as Java, Ruby, and Lisp perform automatic garbage collection that releases memory for objects that have been deallocated.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/125.html
• https://cwe.mitre.org/data/definitions/130.html
• https://cwe.mitre.org/data/definitions/131.html
• https://cwe.mitre.org/data/definitions/494.html
• https://cwe.mitre.org/data/definitions/495.html
• https://cwe.mitre.org/data/definitions/496.html
• https://cwe.mitre.org/data/definitions/666.html

References

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