CVE-2024-38570

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

gfs2: Fix potential glock use-after-free on unmount

When a DLM lockspace is released and there ares still locks in that lockspace, DLM will unlock those locks automatically. Commit fb6791d100d1b started exploiting this behavior to speed up filesystem unmount: gfs2 would simply free glocks it didnt want to unlock and then release the lockspace. This didnt take the bast callbacks for asynchronous lock contention notifications into account, which remain active until until a lock is unlocked or its lockspace is released.

To prevent those callbacks from accessing deallocated objects, put the glocks that should not be unlocked on the sd_dead_glocks list, release the lockspace, and only then free those glocks.

As an additional measure, ignore unexpected ast and bast callbacks if the receiving glock is dead.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/0636b34b44589b142700ac137b5f69802cfe2e37
• https://git.kernel.org/stable/c/501cd8fabf621d10bd4893e37f6ce6c20523c8ca
• https://git.kernel.org/stable/c/d98779e687726d8f8860f1c54b5687eec5f63a73
• https://git.kernel.org/stable/c/e42e8a24d7f02d28763d16ca7ec5fc6d1f142af0
• https://git.kernel.org/stable/c/0636b34b44589b142700ac137b5f69802cfe2e37
• https://git.kernel.org/stable/c/501cd8fabf621d10bd4893e37f6ce6c20523c8ca
• https://git.kernel.org/stable/c/d98779e687726d8f8860f1c54b5687eec5f63a73
• https://git.kernel.org/stable/c/e42e8a24d7f02d28763d16ca7ec5fc6d1f142af0