CVE-2024-39476

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

md/raid5: fix deadlock that raid5d() wait for itself to clear MD_SB_CHANGE_PENDING

Xiao reported that lvm2 test lvconvert-raid-takeover.sh can hang with small possibility, the root cause is exactly the same as commit bed9e27baf52 (Revert md/raid5: Wait for MD_SB_CHANGE_PENDING in raid5d)

However, Dan reported another hang after that, and junxiao investigated the problem and found out that this is caused by plugged bio cant issue from raid5d().

Current implementation in raid5d() has a weird dependence:

1. md_check_recovery() from raid5d() must hold reconfig_mutex to clear MD_SB_CHANGE_PENDING;
2. raid5d() handles IO in a deadloop, until all IO are issued;
3. IO from raid5d() must wait for MD_SB_CHANGE_PENDING to be cleared;

This behaviour is introduce before v2.6, and for consequence, if other context hold reconfig_mutex, and md_check_recovery() cant update super_block, then raid5d() will waste one cpu 100% by the deadloop, until reconfig_mutex is released.

Refer to the implementation from raid1 and raid10, fix this problem by skipping issue IO if MD_SB_CHANGE_PENDING is still set after md_check_recovery(), daemon thread will be woken up when reconfig_mutex is released. Meanwhile, the hang problem will be fixed as well.

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/098d54934814dd876963abfe751c3b1cf7fbe56a
• https://git.kernel.org/stable/c/151f66bb618d1fd0eeb84acb61b4a9fa5d8bb0fa
• https://git.kernel.org/stable/c/3f8d5e802d4cedd445f9a89be8c3fd2d0e99024b
• https://git.kernel.org/stable/c/634ba3c97ec413cb10681c7b196db43ee461ecf4
• https://git.kernel.org/stable/c/aa64464c8f4d2ab92f6d0b959a1e0767b829d787
• https://git.kernel.org/stable/c/b32aa95843cac6b12c2c014d40fca18aef24a347
• https://git.kernel.org/stable/c/cd2538e5af495b3c747e503db346470fc1ffc447
• https://git.kernel.org/stable/c/e332a12f65d8fed8cf63bedb4e9317bb872b9ac7