Bug 2541106 (CVE-2026-98047)

Summary: CVE-2026-98047 kernel: bpf: Check ancestor frames for rbtree callbacks
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 BPF (Berkeley Packet Filter) verifier, which may allow a local attacker to cause a denial of service (DoS) or potentially escalate privileges. When verifying red-black tree (rbtree) callbacks, the verifier fails to enforce callback restrictions across nested subprogram call frames. A local user capable of loading BPF programs can exploit this issue to bypass safety checks and alter locked tree nodes, resulting in freed memory being linked back into the tree. This behavior causes kernel memory corruption and can lead to a system crash.
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Description OSIDB Bzimport 2026-09-25 10:48:53 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf: Check ancestor frames for rbtree callbacks

bpf_rbtree_add() invokes its comparator while the caller holds the root
lock. The native insertion code retains raw parent and link pointers across
the callback, so the verifier prohibits unlocking, consuming tree nodes,
or changing RCU state from that callback.

in_rbtree_lock_required_cb() only checks the innermost verifier frame.
Static subprogram calls are permitted while holding a spin lock, and such a
call pushes a frame without in_callback_fn set. Consequently, all callback
restrictions disappear in the nested frame. The subprogram can unlock the
tree, remove and drop the node being compared, then relock. Native insertion
resumes with the stale parent pointer and links freed memory into the tree.

Walk all active frames for the rbtree callback instead. Benign static
subprograms remain permitted, while callback restrictions follow execution
into nested frames.
Comment 1 Keith Grant 2026-09-28 23:19:18 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98047.mbox