{"id":"CVE-2026-98084","state":"PUBLISHED","title":"bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks","description":"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 < 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'.","publishedAt":"2026-09-25T10:24:19.881Z","updatedAt":"2026-10-21T12:54:25.939Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd","status":"affected","lessThan":"1ac58dab0a83d2c64e3b807a3a0b399f17a74110","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"cdc93c6370f792d0649df2a145ac0cdcd430e411","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"3a39bc9707fbd1bef4df7318a9d02222741dda5b","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"f83890dfed9efc5e19df1dbc1ad707a142936923","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"e3e4f66cc4b72333d0886ae2673c360248987889","versionType":"git"},{"version":"6.6.15","status":"affected","lessThan":"6.6.160","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/backtrack.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.7","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/backtrack.c"]}],"references":["https://git.kernel.org/stable/c/1ac58dab0a83d2c64e3b807a3a0b399f17a74110","https://git.kernel.org/stable/c/cdc93c6370f792d0649df2a145ac0cdcd430e411","https://git.kernel.org/stable/c/3a39bc9707fbd1bef4df7318a9d02222741dda5b","https://git.kernel.org/stable/c/f83890dfed9efc5e19df1dbc1ad707a142936923","https://git.kernel.org/stable/c/e3e4f66cc4b72333d0886ae2673c360248987889"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98084.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98084","state":"PUBLISHED","datePublished":"2026-09-25T10:24:19.881Z","dateUpdated":"2026-10-21T12:54:25.939Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:19:56.075Z"},"containers":{"cna":{"title":"bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks","descriptions":[{"lang":"en","value":"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 < 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'."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd","status":"affected","lessThan":"1ac58dab0a83d2c64e3b807a3a0b399f17a74110","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"cdc93c6370f792d0649df2a145ac0cdcd430e411","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"3a39bc9707fbd1bef4df7318a9d02222741dda5b","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"f83890dfed9efc5e19df1dbc1ad707a142936923","versionType":"git"},{"version":"ab5cfac139ab8576fb54630d4cca23c3e690ee90","status":"affected","lessThan":"e3e4f66cc4b72333d0886ae2673c360248987889","versionType":"git"},{"version":"6.6.15","status":"affected","lessThan":"6.6.160","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/backtrack.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.7","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/backtrack.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/1ac58dab0a83d2c64e3b807a3a0b399f17a74110"},{"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"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-21T12:54:25.939Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.15","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"7.2.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}