{"id":"CVE-2026-98813","summary":"bpf: Hold map BTF for the memory allocator destructor record","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Hold map BTF for the memory allocator destructor record\n\nbpf_ma_set_dtor() duplicates map-\u003erecord so that the bpf_mem_alloc\ndestructor can release the special fields of hash and rhash map elements\nonce the allocator frees them for good. btf_record_dup() only acquires\nreferences on kernel and module BTF. Fields whose types live in the map\nBTF keep pointing into it: a kptr to a local type refers to map-\u003ebtf,\nand a list_head or rb_root field carries a value_rec owned by the struct\nmeta table of map-\u003ebtf.\n\nThat borrowed state can outlive the map. When RCU callbacks are still in\nflight, bpf_mem_alloc_destroy() copies the allocator and defers the final\ndrain, together with the destructor context, to a workqueue.\nbpf_map_free() then frees map-\u003erecord and drops the map's BTF reference\nas soon as map_free() returns. Once the program that loaded the BTF is\ngone as well, the BTF is freed while the worker still uses the\nduplicate. The worker dereferences it through btf_is_kernel() and\nbtf_find_struct_meta() in bpf_obj_free_fields() when destroying elements\nthat were freed under RCU, and through btf_is_kernel() in\nbtf_record_free() when releasing the context itself:\n\n  BUG: KASAN: slab-use-after-free in btf_is_kernel+0x19/0x30\n  Read of size 1 at addr ffff88811505dce8 by task kworker/u16:2/50\n  Workqueue: events_unbound free_mem_alloc_deferred\n  Call Trace:\n   btf_is_kernel+0x19/0x30\n   btf_record_free+0xc7/0xf0\n   htab_dtor_ctx_free+0x1a/0x30\n   free_mem_alloc_no_barrier+0x39/0x230\n   free_mem_alloc_deferred+0x2a/0x40\n   process_scheduled_works+0x5ce/0x9d0\n   worker_thread+0x42a/0x5e0\n   kthread+0x1f5/0x230\n   ret_from_fork+0x1dd/0x390\n   ret_from_fork_asm+0x1a/0x30\n\n  Allocated by task 358:\n   __kmalloc_cache_noprof+0x287/0x510\n   btf_new_fd+0xf7/0x3d0\n   __sys_bpf+0x487/0x840\n\n  Freed by task 0:\n   kfree+0x186/0x560\n   rcu_core+0x6f6/0xd40\n\nFreeing a map that still holds more elements than the allocator's high\nwatermark is enough to get there, because the bulk free during teardown\nqueues the RCU callback that makes bpf_mem_alloc_destroy() defer.\nNon-preallocated hash maps and resizable hash maps both register the\ndestructor and are affected alike.\n\nKeep one reference on the map BTF in the destructor context. Every\nnon-kernel pointer in the duplicated record is either map-\u003ebtf or memory\nowned by it, so a single reference covers kptrs, list heads, and rb\nroots, and mirrors what bpf_map_meta_alloc() does for the duplicated\nrecord of an inner map. Release it only after the duplicated record has\nbeen freed: the worker is preemptible and not in an RCU read-side\ncritical section, so dropping the last reference first would let the\nBTF be freed while btf_record_free() still reads its fields.","modified":"2026-10-20T02:30:54.838480919Z","published":"2026-10-18T15:48:59.745Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98813.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/ab39974240a0cff765f3bb9cce81d8001ffdb144"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b506f5699e145196ee29d76cf1ca1cbb2202c055"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98813.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98813"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"1df97a7453eec80c1912c2d0360290a3970a7671"},{"fixed":"b506f5699e145196ee29d76cf1ca1cbb2202c055"},{"fixed":"ab39974240a0cff765f3bb9cce81d8001ffdb144"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6.12.112"},{"fixed":"6.13"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6.18.55"},{"fixed":"6.19"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"451a84a3ad3c897c03181af433e7c98640730f1f"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"51a17f0ce19c4ee2a25cf16c93490d509b1ebb0a"}]}],"versions":["v6.12.113","v6.12.112","v6.18.57","v6.18.56","v6.18.55"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98813.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"7.0.0"},{"fixed":"7.2.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98813.json"}}],"schema_version":"1.9.0"}