Bug 2420280 (CVE-2023-53810)

Summary:	CVE-2023-53810 kernel: blk-mq: release crypto keyslot before reporting I/O complete
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	Keywords:	Security
Target Milestone:	---
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was identified in the block multi-queue (blk-mq) subsystem of the Linux kernel where the crypto keyslot associated with a block I/O request could be released after upper layers have been notified that the I/O operation completed. Under certain conditions, this could lead to a use-after-free of the crypto keyslot object if a filesystem segment attempts to evict a crypto key while I/O is still effectively using it.	Story Points:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2025-12-09 01:05:31 UTC

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

blk-mq: release crypto keyslot before reporting I/O complete

Once all I/O using a blk_crypto_key has completed, filesystems can call
blk_crypto_evict_key().  However, the block layer currently doesn't call
blk_crypto_put_keyslot() until the request is being freed, which happens
after upper layers have been told (via bio_endio()) the I/O has
completed.  This causes a race condition where blk_crypto_evict_key()
can see 'slot_refs != 0' without there being an actual bug.

This makes __blk_crypto_evict_key() hit the
'WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)' and return without
doing anything, eventually causing a use-after-free in
blk_crypto_reprogram_all_keys().  (This is a very rare bug and has only
been seen when per-file keys are being used with fscrypt.)

There are two options to fix this: either release the keyslot before
bio_endio() is called on the request's last bio, or make
__blk_crypto_evict_key() ignore slot_refs.  Let's go with the first
solution, since it preserves the ability to report bugs (via
WARN_ON_ONCE) where a key is evicted while still in-use.

Comment 1 Alexander B 2025-12-10 04:45:02 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025120944-CVE-2023-53810-e48e@gregkh/T