CVE-2025-21893

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

keys: Fix UAF in key_put()

Once a keys reference count has been reduced to 0, the garbage collector thread may destroy it at any time and so key_put() is not allowed to touch the key after that point. The most key_put() is normally allowed to do is to touch key_gc_work as thats a static global variable.

However, in an effort to speed up the reclamation of quota, this is now done in key_put() once the keys usage is reduced to 0 - but now the code is looking at the key after the deadline, which is forbidden.

Fix this by using a flag to indicate that a key can be gcd now rather than looking at the keys refcount in the garbage collector.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3
• https://git.kernel.org/stable/c/75845c6c1a64483e9985302793dbf0dfa5f71e32
• https://git.kernel.org/stable/c/f6a3cf833188e897c97028cd7b926e3f2cb1a8c0