Bug 2555238 (CVE-2026-98820)

Summary: CVE-2026-98820 kernel: blk-mq: set RQF_USE_SCHED when the operation is known
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's block multi-queue (blk-mq) subsystem. When cached input/output (I/O) requests originally allocated for passthrough commands are reused for standard read or write operations, scheduler flags are not properly updated. This failure bypasses required scheduler initialization and cleanup routines, leading to internal resource leaks in certain I/O schedulers like Kyber. A local attacker could exploit this flaw to stall storage queues, resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-10-18 16:03:54 UTC 
In the Linux kernel, the following vulnerability has been resolved:

blk-mq: set RQF_USE_SCHED when the operation is known

The cached requests are allocated for one operation but can be handed
out for another. A passthrough command has RQF_USE_SCHED cleared, so
using those flags for a subsequent read/write bio will insert it into
the scheduler without ->prepare_request() and frees it without
->finish_request(). For kyber, this leaks the domain token acquired at
dispatch and stalls the queue.

Don't set RQF_USE_SCHED based on the first operation the batch happened
to be allocated for. Instead, set it after the request is claimed by an
operation. Introduce a helper function, blk_mq_rq_late_init() for this,
and absorb blk_mq_rq_time_init() since the two run together.
Comment 1 Mauro Matteo Cascella 2026-10-23 19:23:30 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98820.mbox