Bug 2356295 (CVE-2025-21893)

Summary: CVE-2025-21893 kernel: keys: Fix UAF in key_put()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
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Hardware: All   
OS: Linux   
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Description OSIDB Bzimport 2025-03-31 20:01:04 UTC 
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.
Comment 1 Avinash Hanwate 2025-04-01 04:01:10 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025033126-CVE-2025-21893-f2b4@gregkh/T
Comment 3 errata-xmlrpc 2025-06-16 07:44:06 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10

Via RHSA-2025:9079 https://access.redhat.com/errata/RHSA-2025:9079