{"id":"AZL-104294","summary":"CVE-2026-98084 affecting package kernel 6.6.157.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: backtracking shouldn't clear outer frame R1-R5 for callbacks\n\nWhen processing calls to bpf_loop() verifier marks R1 (and R4) as\nprecise. R1 tracks loop iterations number and because of the\n'callback_depth \u003c R1' mechanics in check_helper_call() must be marked\nprecise. However, precision propagation for R1 was broken,\nwhen bpf_loop() call was verified on a second iteration.\n\nConsider the following verification trace:\n- main: bpf_loop(nr_loops, callback ...)\n- callback: BPF_EXIT\n- main: bpf_loop(nr_loops, callback ...)\n- ...\n\nWhile the first visit of the call to bpf_loop() propagated R1\nprecision as expected, the second call to mark_chain_precision() in\nthe check_helper_call() set R1, but it was immediately reset when\nbacktrack_insn() processed preceding BPF_EXIT in the loop deleted in\nthis patch.\n\nBecause of that, the second visit of the call to bpf_loop() injected\ncheckpoint with R1 not marked as precise. Which could trick the\nverifier into accepting unsafe programs. See the next patch for an\nexample of such program.\n\nCommit is structured in a way to minimize conflicts when\n'bpf' would be eventually merged with 'bpf-next'.","modified":"2026-09-28T05:39:54Z","published":"2026-09-25T11:17:37Z","upstream":["CVE-2026-98084"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98084"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.157.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-104294.json"}}],"schema_version":"1.9.0"}