UBUNTU-CVE-2025-21893
In the Linux kernel, the following vulnerability has been resolved: keys: Fix UAF in key_put() Once a key's 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 that's a static global variable. However, in an effort to speed up the reclamation of quota, this is now done in key_put() once the key's 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 gc'd now rather than looking at the key's refcount in the garbage collector.
02 / AFFECTED SOFTWARE
Affected packages
5 explicit affected versions
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26 explicit affected versions
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6 explicit affected versions
5 explicit affected versions
13 explicit affected versions
7 explicit affected versions
6 explicit affected versions
10 explicit affected versions
14 explicit affected versions
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3 explicit affected versions
16 explicit affected versions
6 explicit affected versions
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12 explicit affected versions
7 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: keys: Fix UAF in key_put() Once a key's 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 that's a static global variable. However, in an effort to speed up the reclamation of quota, this is now done in key_put() once the key's 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 gc'd now rather than looking at the key's refcount in the garbage collector.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/75845c6c1a64483e9985302793dbf0dfa5f71e32
- https://git.kernel.org/stable/c/6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3
- https://git.kernel.org/stable/c/75845c6c1a64483e9985302793dbf0dfa5f71e32
- https://git.kernel.org/stable/c/f6a3cf833188e897c97028cd7b926e3f2cb1a8c0
- https://ubuntu.com/security/CVE-2025-21893
- https://ubuntu.com/security/notices/USN-7605-1
- https://ubuntu.com/security/notices/USN-7605-2
- https://ubuntu.com/security/notices/USN-7606-1
- https://ubuntu.com/security/notices/USN-7628-1
- https://www.cve.org/CVERecord?id=CVE-2025-21893