Bug 2541135 (CVE-2026-98038)

Summary: CVE-2026-98038 kernel: bpf: Keep refcount_acquire nullable for borrowed RCU kptrs
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
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 Berkeley Packet Filter (BPF) subsystem. When validating programs that manage shared reference-counted objects, the BPF verifier incorrectly treats borrowed references as always valid and fails to require null-pointer checks. A local user can exploit this vulnerability by loading a crafted BPF program, triggering a null-pointer dereference that causes a kernel crash and Denial of Service (DoS).
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-09-25 10:51:22 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf: Keep refcount_acquire nullable for borrowed RCU kptrs

bpf_refcount_acquire() is fallible for a borrowed reference because the
object may have reached a zero refcount. The verifier therefore keeps
KF_RET_NULL on the return value unless the argument is an owning reference.

An RCU-protected load of a local kptr is marked MEM_ALLOC, but it only
receives NON_OWN_REF when the pointee contains a graph node. A refcounted
object without a graph node consequently looks like an owning reference
even though the loaded register has no acquired reference state. If the
program drops the last real reference while remaining in the RCU critical
section, refcount_inc_not_zero() returns NULL while the verifier treats the
result as non-NULL.

Only classify the argument as owning when it is backed by a verifier-tracked
reference. This retains the non-NULL return for pointers from bpf_obj_new(),
bpf_kptr_xchg(), or an earlier successful acquisition, while requiring a
NULL check for borrowed RCU kptrs.

[ kkd: Rewrote commit log ]
Comment 1 Keith Grant 2026-09-28 22:40:05 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98038.mbox