CVE-2026-98084 (GCVE-0-2026-98084)
Vulnerability from cvelistv5
Published
2026-09-25 10:24
Modified
2026-10-21 12:54
Severity ?
Summary
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'.
References
Impacted products
Vendor Product Version
Linux Linux Version: b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd
Version: ab5cfac139ab8576fb54630d4cca23c3e690ee90
Version: ab5cfac139ab8576fb54630d4cca23c3e690ee90
Version: ab5cfac139ab8576fb54630d4cca23c3e690ee90
Version: ab5cfac139ab8576fb54630d4cca23c3e690ee90
Version: 6.6.15   ≤
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: backtracking shouldn\u0027t 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\u0027callback_depth \u003c R1\u0027 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\u0027bpf\u0027 would be eventually merged with \u0027bpf-next\u0027."
        }
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      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:54:25.939Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/1ac58dab0a83d2c64e3b807a3a0b399f17a74110"
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          "url": "https://git.kernel.org/stable/c/cdc93c6370f792d0649df2a145ac0cdcd430e411"
        },
        {
          "url": "https://git.kernel.org/stable/c/3a39bc9707fbd1bef4df7318a9d02222741dda5b"
        },
        {
          "url": "https://git.kernel.org/stable/c/f83890dfed9efc5e19df1dbc1ad707a142936923"
        },
        {
          "url": "https://git.kernel.org/stable/c/e3e4f66cc4b72333d0886ae2673c360248987889"
        }
      ],
      "title": "bpf: backtracking shouldn\u0027t clear outer frame R1-R5 for callbacks",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98084",
    "datePublished": "2026-09-25T10:24:19.881Z",
    "dateReserved": "2026-09-25T10:19:56.075Z",
    "dateUpdated": "2026-10-21T12:54:25.939Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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