Bug 2554906 (CVE-2026-98463)

Summary: CVE-2026-98463 kernel: sched_ext: Derive SCX_RQ_IN_WAKEUP from the core enqueue flags
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 sched_ext (extensible scheduler) subsystem. Improper handling of wakeup enqueue flags during remote task activation can cause a deferred action request to remain pending after the scheduler is disabled. When a new scheduler initializes and processes deferred actions, it dereferences pointers pointing into freed memory. A local attacker could exploit this use-after-free condition to cause a Denial of Service (DoS) via a kernel crash or potentially corrupt memory.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-10-18 15:27:15 UTC 
In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Derive SCX_RQ_IN_WAKEUP from the core enqueue flags

schedule_deferred_locked() skips scheduling a deferred action while
SCX_RQ_IN_WAKEUP is set and relies on the task_woken_scx() call that follows
a wakeup enqueue to run it. enqueue_task_scx() sets the flag from the merged
enqueue flags, which include the flags stashed for a remote activation.
move_remote_task_to_local_dsq() thus sets SCX_RQ_IN_WAKEUP on the
destination rq when the moved task was woken up, although no
task_woken_scx() follows that activation.

An IMMED insert into a busy destination requests a local reenqueue during
that enqueue. The request gets linked but not scheduled and stays pending
until an unrelated wakeup or preemption on that CPU runs the deferred
actions. The IMMED task sits behind the running task in the meantime. If
nothing runs them before the scheduler is disabled, the request outlives the
scheduler and points into its freed per-cpu area, which the next scheduler
dereferences from run_deferred().

Test the core enqueue flags for the wakeup bit. Only the core's wakeup path
is followed by task_woken_scx().