{"id":"CVE-2026-89579","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-89579","summary":"bpf: Harden bloom filter sizing and indexing on 32-bit kernels","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Harden bloom filter sizing and indexing on 32-bit kernels\n\nbloom_map_alloc() has two 32-bit-specific problems when the computed\nbitmap reaches the U32_MAX fallback case.\n\nFirst, BITS_TO_BYTES(U32_MAX) is evaluated with 32-bit arithmetic. The\naddition performed by DIV_ROUND_UP wraps, so the map allocates only the\nfixed-size bloom filter object while keeping bitset_mask == U32_MAX.\nSubsequent updates can then write past the allocated object.\n\nSecond, fixing only the allocation size is not sufficient. The bloom hash\nis a u32, but set_bit() takes a signed long bit number and x86 test_bit()\neventually feeds the index to variable_test_bit(long, ...). On 32-bit\nkernels, hashes in [0x80000000, U32_MAX] therefore become negative bit\noffsets. x86 bt/bts with a memory operand interpret those offsets relative\nto the supplied base, so a map with bitset_mask == U32_MAX can read or\nwrite before bloom->bitset even after allocating the full 512 MiB bitmap.\n\nKeep the U32_MAX fallback, but split each hash into a word pointer and an\nin-word bit number before calling test_bit() or set_bit(). The bitops\nargument is then always in [0, BITS_PER_LONG - 1], while BIT_WORD(h) still\nselects the intended word in the full bitmap.\n\nCompute the bitset size from (u64)bitset_mask + 1 before passing the final\nsize to bpf_map_area_alloc(). This fixes the original under-allocation and\nkeeps the allocated storage consistent with the addressable bitset.\n\nExploitation note: local privilege escalation is possible on a 32-bit x86\nkernel using the under-allocation bug from a binary with CAP_BPF.","published":"2026-09-11T19:44:46.110Z","modified":"2026-09-14T03:46:12.903518891Z","cvss":{"score":7.8,"severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.12.109"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/11c1e836710dcba03e50454a4eedfdbaf8d3050e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/272fcb4ba6fab678db0eb966dc81c4c804bef64a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3b7a13eccfcf97714ffc1ca6aa663d66d4a30e29"},{"type":"WEB","url":"https://git.kernel.org/stable/c/dff481e12b3f127739f6a4ea7cef2c25dc12e056"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89579.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89579"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-14T03:46:12.903518891Z"}}