{"id":"CVE-2026-98061","summary":"bpf: Reject tail calls directly from callback frames","details":"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.","modified":"2026-09-26T03:48:32.431558135Z","published":"2026-09-25T10:24:06.001Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98061.json","cna_assigner":"Linux"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd"},{"type":"WEB","url":"https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025"},{"type":"WEB","url":"https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98061.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98061"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"a6c22c91b6284e4713c0cf5b20ab3c9c71b77ae8"},{"fixed":"617c8266e49f45747f71e74177646a63f72b7025"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"e3245f8990431950d20631c72236d4e8cb2dcde8"},{"fixed":"96d31b28263c429a56e4de85bcf744a5c320b3a3"},{"fixed":"266aa4ad0b2e82397cd9045752c9bff03d98eddd"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6.18.2"},{"fixed":"6.18.53"}]}],"versions":["v6.18.52","v6.18.51","v6.18.50","v6.18.49","v6.18.48","v6.18.47","v6.18.46","v6.18.45","v6.18.44","v6.18.43","v6.18.42","v6.18.41","v6.18.40","v6.18.39","v6.18.38","v6.18.37","v6.18.36","v6.18.35","v6.18.34","v6.18.33","v6.18.32","v6.18.31","v6.18.30","v6.18.29","v6.18.28","v6.18.27","v6.18.26","v6.18.25","v6.18.24","v6.18.23","v6.18.22","v6.18.21","v6.18.20","v6.18.19","v6.18.18","v6.18.17","v6.18.16","v6.18.15","v6.18.14","v6.18.13","v6.18.12","v6.18.11","v6.18.10","v6.18.9","v6.18.8","v6.18.7","v6.18.6","v6.18.5","v6.18.4","v6.18.3","v6.18.2"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98061.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.18.53"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.7"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98061.json"}}],"schema_version":"1.9.0"}