CVE-2026-98084
UnknownSummary
In the Linux kernel, the precision backtracking for bpf_loop() calls had a bug: on the second visit of the call, the precision of register R1 (loop counter) was reset by processing the preceding BPF_EXIT. This resulted in injecting a checkpoint without R1 marked as precise, potentially allowing the verifier to accept unsafe programs.
Risk Assessment
The vulnerability could allow the BPF verifier to accept unsafe programs, potentially leading to privilege escalation or kernel security compromise.
Recommendation
It is recommended to update the Linux kernel to a version with the fix that removes the erroneous clearing of R1-R5 precision in the outer frame for callbacks.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks When processing calls to bpf_loop() verifier marks R1 (and R4) as precise. R1 tracks loop iterations number and because of the 'callback_depth < R1' mechanics in check_helper_call() must be marked precise. However, precision propagation for R1 was broken, when bpf_loop() call was verified on a second iteration. Consider the following verification trace: - main: bpf_loop(nr_loops, callback ...) - callback: BPF_EXIT - main: bpf_loop(nr_loops, callback ...) - ... While the first visit of the call to bpf_loop() propagated R1 precision as expected, the second call to mark_chain_precision() in the check_helper_call() set R1, but it was immediately reset when backtrack_insn() processed preceding BPF_EXIT in the loop deleted in this patch. Because of that, the second visit of the call to bpf_loop() injected checkpoint with R1 not marked as precise. Which could trick the verifier into accepting unsafe programs. See the next patch for an example of such program. Commit is structured in a way to minimize conflicts when 'bpf' would be eventually merged with 'bpf-next'.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS