UBUNTU-CVE-2026-98084: High severity ubuntu/linux-hwe-edge vulnerability

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 bpfloop() verifier marks R1 (and R4) as precise. R1 tracks loop iterations number and because of the 'callbackdepth < R1' mechanics in checkhelpercall() must be marked precise. However, precision propagation for R1 was broken, when bpfloop() call was verified on a second iteration. Consider the following verification trace: - main: bpfloop(nrloops, callback ...) - callback: BPFEXIT - main: bpfloop(nrloops, callback ...) - ... While the first visit of the call to bpfloop() propagated R1 precision as expected, the second call to markchainprecision() in the checkhelpercall() set R1, but it was immediately reset when backtrackinsn() processed preceding BPFEXIT in the loop deleted in this patch. Because of that, the second visit of the call to bpfloop() 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'.