{"id":"CVE-2026-98061","state":"PUBLISHED","title":"bpf: Reject tail calls directly from callback frames","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject tail calls directly from callback frames\n\nA tail call from a non-zero frame is modeled as a return from that frame.\nThe verifier makes R0 unknown and calls prepare_func_exit() for the taken\nbranch.\n\nWhen the current frame is a synchronous callback, prepare_func_exit()\nenforces the callback return-value contract and marks R0 precise. Since the\ntail-call path synthesized R0 rather than deriving it from an instruction,\nprecision backtracking reaches the callback-calling instruction with R0\nstill requested and triggers the \"callback unexpected regs\" verifier bug.\nA CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.\n\nTail calls reachable from callbacks are already rejected later by\ncheck_max_stack_depth(). Reject a tail call made directly by a callback\nbefore constructing the inconsistent return state, using the existing\ndiagnostic. Tail calls from ordinary subprograms keep their current\nbehavior.","publishedAt":"2026-09-25T10:24:06.001Z","updatedAt":"2026-10-19T09:13:09.930Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a6c22c91b6284e4713c0cf5b20ab3c9c71b77ae8","status":"affected","lessThan":"617c8266e49f45747f71e74177646a63f72b7025","versionType":"git"},{"version":"e3245f8990431950d20631c72236d4e8cb2dcde8","status":"affected","lessThan":"96d31b28263c429a56e4de85bcf744a5c320b3a3","versionType":"git"},{"version":"e3245f8990431950d20631c72236d4e8cb2dcde8","status":"affected","lessThan":"266aa4ad0b2e82397cd9045752c9bff03d98eddd","versionType":"git"},{"version":"6.18.2","status":"affected","lessThan":"6.18.53","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/verifier.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.19","versionType":"semver"},{"version":"6.18.53","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/verifier.c"]}],"references":["https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025","https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3","https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98061.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98061","state":"PUBLISHED","datePublished":"2026-09-25T10:24:06.001Z","dateUpdated":"2026-10-19T09:13:09.930Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:19:56.073Z"},"containers":{"cna":{"title":"bpf: Reject tail calls directly from callback frames","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject tail calls directly from callback frames\n\nA tail call from a non-zero frame is modeled as a return from that frame.\nThe verifier makes R0 unknown and calls prepare_func_exit() for the taken\nbranch.\n\nWhen the current frame is a synchronous callback, prepare_func_exit()\nenforces the callback return-value contract and marks R0 precise. Since the\ntail-call path synthesized R0 rather than deriving it from an instruction,\nprecision backtracking reaches the callback-calling instruction with R0\nstill requested and triggers the \"callback unexpected regs\" verifier bug.\nA CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.\n\nTail calls reachable from callbacks are already rejected later by\ncheck_max_stack_depth(). Reject a tail call made directly by a callback\nbefore constructing the inconsistent return state, using the existing\ndiagnostic. Tail calls from ordinary subprograms keep their current\nbehavior."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a6c22c91b6284e4713c0cf5b20ab3c9c71b77ae8","status":"affected","lessThan":"617c8266e49f45747f71e74177646a63f72b7025","versionType":"git"},{"version":"e3245f8990431950d20631c72236d4e8cb2dcde8","status":"affected","lessThan":"96d31b28263c429a56e4de85bcf744a5c320b3a3","versionType":"git"},{"version":"e3245f8990431950d20631c72236d4e8cb2dcde8","status":"affected","lessThan":"266aa4ad0b2e82397cd9045752c9bff03d98eddd","versionType":"git"},{"version":"6.18.2","status":"affected","lessThan":"6.18.53","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/verifier.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.19","versionType":"semver"},{"version":"6.18.53","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/verifier.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025"},{"url":"https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3"},{"url":"https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T09:13:09.930Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18.2","versionEndExcluding":"6.18.53"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19","versionEndExcluding":"7.2.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}