{"id":"CVE-2026-97420","summary":"bpf: NUL-terminate replaced sysctl value","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: NUL-terminate replaced sysctl value\n\nWhen writing to sysctls, proc_sys_call_handler() guarantees that the\nbuffer passed to proc handlers is NUL-terminated. If\nbpf_sysctl_set_new_value() replaces the pending sysctl value, it can\nhand a replacement buffer directly to proc handlers. However, the\nhelper currently copies only buf_len bytes into that buffer without\nappending a NUL terminator, leaving downstream parsers vulnerable to\nout-of-bounds access.\n\nFix this by appending a '\\0' after the replaced value to restore the\nexpected sysctl semantics. Since the helper already rejects buf_len\ngreater than PAGE_SIZE - 1, there is always room for the extra byte.\n\nReproduced in a QEMU x86_64 guest booted with KASAN while exercising\nthe sysctl replacement path with a cgroup/sysctl BPF program. The\nreproducer targets `/proc/sys/net/core/flow_limit_cpu_bitmap`, fills\nthe original user write buffer with non-zero bytes, and overrides the\nsysctl value so the replacement buffer lacks a terminating NUL. Under\nthat setup, the pre-fix kernel reported:\n\n  BUG: KASAN: slab-out-of-bounds in strnchrnul+0x72/0x90\n  Read of size 1 at addr ffff88800de57000 by task repro_patch3/66\n  CPU: 0 UID: 0 PID: 66 Comm: repro_patch3 Not tainted 7.1.0-rc3-00269-g8370ca1f87cc #6 PREEMPT(lazy)\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014\n  Call Trace:\n   \u003cTASK\u003e\n   dump_stack_lvl+0x68/0xa0\n   print_report+0xcb/0x5e0\n   ? __virt_addr_valid+0x21d/0x3f0\n   ? strnchrnul+0x72/0x90\n   ? strnchrnul+0x72/0x90\n   kasan_report+0xca/0x100\n   ? strnchrnul+0x72/0x90\n   strnchrnul+0x72/0x90\n   bitmap_parse+0x37/0x2e0\n   flow_limit_cpu_sysctl+0xc6/0x840\n   ? __pfx_flow_limit_cpu_sysctl+0x10/0x10\n   ? __kvmalloc_node_noprof+0x5ba/0x870\n   proc_sys_call_handler+0x31d/0x480\n   ? __pfx_proc_sys_call_handler+0x10/0x10\n   ? selinux_file_permission+0x39f/0x500\n   ? lock_is_held_type+0x9e/0x120\n   vfs_write+0x98e/0x1000\n   ...\n   \u003c/TASK\u003e\n  The buggy address is located 0 bytes to the right of\n  allocated 4096-byte region [ffff88800de56000, ffff88800de57000)\nWith this fix applied, rerunning the same sysctl-targeted path yields\nno corresponding KASAN reports.","modified":"2026-09-26T03:48:27.088689855Z","published":"2026-09-24T16:03:30.084Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97420.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/3b2814dd842a565fcf9cc370156e1ba9eae16239"},{"type":"WEB","url":"https://git.kernel.org/stable/c/76c14b10f50eb0afcc76e244562fa2d8c661e224"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a66e3b5bacf38d6ab29fa05a9754f7a114485605"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97420.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-97420"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"32927393dc1ccd60fb2bdc05b9e8e88753761469"},{"fixed":"76c14b10f50eb0afcc76e244562fa2d8c661e224"},{"fixed":"3b2814dd842a565fcf9cc370156e1ba9eae16239"},{"fixed":"a66e3b5bacf38d6ab29fa05a9754f7a114485605"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97420.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.8.0"},{"fixed":"6.12.111"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.53"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97420.json"}}],"schema_version":"1.9.0"}