Description
In the Linux kernel, the following vulnerability has been resolved:
bpf: Hold map BTF for the memory allocator destructor record
bpf_ma_set_dtor() duplicates map->record so that the bpf_mem_alloc
destructor can release the special fields of hash and rhash map elements
once the allocator frees them for good. btf_record_dup() only acquires
references on kernel and module BTF. Fields whose types live in the map
BTF keep pointing into it: a kptr to a local type refers to map->btf,
and a list_head or rb_root field carries a value_rec owned by the struct
meta table of map->btf.
That borrowed state can outlive the map. When RCU callbacks are still in
flight, bpf_mem_alloc_destroy() copies the allocator and defers the final
drain, together with the destructor context, to a workqueue.
bpf_map_free() then frees map->record and drops the map's BTF reference
as soon as map_free() returns. Once the program that loaded the BTF is
gone as well, the BTF is freed while the worker still uses the
duplicate. The worker dereferences it through btf_is_kernel() and
btf_find_struct_meta() in bpf_obj_free_fields() when destroying elements
that were freed under RCU, and through btf_is_kernel() in
btf_record_free() when releasing the context itself:
BUG: KASAN: slab-use-after-free in btf_is_kernel+0x19/0x30
Read of size 1 at addr ffff88811505dce8 by task kworker/u16:2/50
Workqueue: events_unbound free_mem_alloc_deferred
Call Trace:
btf_is_kernel+0x19/0x30
btf_record_free+0xc7/0xf0
htab_dtor_ctx_free+0x1a/0x30
free_mem_alloc_no_barrier+0x39/0x230
free_mem_alloc_deferred+0x2a/0x40
process_scheduled_works+0x5ce/0x9d0
worker_thread+0x42a/0x5e0
kthread+0x1f5/0x230
ret_from_fork+0x1dd/0x390
ret_from_fork_asm+0x1a/0x30
Allocated by task 358:
__kmalloc_cache_noprof+0x287/0x510
btf_new_fd+0xf7/0x3d0
__sys_bpf+0x487/0x840
Freed by task 0:
kfree+0x186/0x560
rcu_core+0x6f6/0xd40
Freeing a map that still holds more elements than the allocator's high
watermark is enough to get there, because the bulk free during teardown
queues the RCU callback that makes bpf_mem_alloc_destroy() defer.
Non-preallocated hash maps and resizable hash maps both register the
destructor and are affected alike.
Keep one reference on the map BTF in the destructor context. Every
non-kernel pointer in the duplicated record is either map->btf or memory
owned by it, so a single reference covers kptrs, list heads, and rb
roots, and mirrors what bpf_map_meta_alloc() does for the duplicated
record of an inner map. Release it only after the duplicated record has
been freed: the worker is preemptible and not in an RCU read-side
critical section, so dropping the last reference first would let the
BTF be freed while btf_record_free() still reads its fields.
bpf: Hold map BTF for the memory allocator destructor record
bpf_ma_set_dtor() duplicates map->record so that the bpf_mem_alloc
destructor can release the special fields of hash and rhash map elements
once the allocator frees them for good. btf_record_dup() only acquires
references on kernel and module BTF. Fields whose types live in the map
BTF keep pointing into it: a kptr to a local type refers to map->btf,
and a list_head or rb_root field carries a value_rec owned by the struct
meta table of map->btf.
That borrowed state can outlive the map. When RCU callbacks are still in
flight, bpf_mem_alloc_destroy() copies the allocator and defers the final
drain, together with the destructor context, to a workqueue.
bpf_map_free() then frees map->record and drops the map's BTF reference
as soon as map_free() returns. Once the program that loaded the BTF is
gone as well, the BTF is freed while the worker still uses the
duplicate. The worker dereferences it through btf_is_kernel() and
btf_find_struct_meta() in bpf_obj_free_fields() when destroying elements
that were freed under RCU, and through btf_is_kernel() in
btf_record_free() when releasing the context itself:
BUG: KASAN: slab-use-after-free in btf_is_kernel+0x19/0x30
Read of size 1 at addr ffff88811505dce8 by task kworker/u16:2/50
Workqueue: events_unbound free_mem_alloc_deferred
Call Trace:
btf_is_kernel+0x19/0x30
btf_record_free+0xc7/0xf0
htab_dtor_ctx_free+0x1a/0x30
free_mem_alloc_no_barrier+0x39/0x230
free_mem_alloc_deferred+0x2a/0x40
process_scheduled_works+0x5ce/0x9d0
worker_thread+0x42a/0x5e0
kthread+0x1f5/0x230
ret_from_fork+0x1dd/0x390
ret_from_fork_asm+0x1a/0x30
Allocated by task 358:
__kmalloc_cache_noprof+0x287/0x510
btf_new_fd+0xf7/0x3d0
__sys_bpf+0x487/0x840
Freed by task 0:
kfree+0x186/0x560
rcu_core+0x6f6/0xd40
Freeing a map that still holds more elements than the allocator's high
watermark is enough to get there, because the bulk free during teardown
queues the RCU callback that makes bpf_mem_alloc_destroy() defer.
Non-preallocated hash maps and resizable hash maps both register the
destructor and are affected alike.
Keep one reference on the map BTF in the destructor context. Every
non-kernel pointer in the duplicated record is either map->btf or memory
owned by it, so a single reference covers kptrs, list heads, and rb
roots, and mirrors what bpf_map_meta_alloc() does for the duplicated
record of an inner map. Release it only after the duplicated record has
been freed: the worker is preemptible and not in an RCU read-side
critical section, so dropping the last reference first would let the
BTF be freed while btf_record_free() still reads its fields.
Published:
2026-10-18
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
No analysis available yet.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
|||||||||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No remediation available yet.
Tracking
Sign in to view the affected projects.
Advisories
No advisories yet.
References
History
Sun, 18 Oct 2026 16:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: bpf: Hold map BTF for the memory allocator destructor record bpf_ma_set_dtor() duplicates map->record so that the bpf_mem_alloc destructor can release the special fields of hash and rhash map elements once the allocator frees them for good. btf_record_dup() only acquires references on kernel and module BTF. Fields whose types live in the map BTF keep pointing into it: a kptr to a local type refers to map->btf, and a list_head or rb_root field carries a value_rec owned by the struct meta table of map->btf. That borrowed state can outlive the map. When RCU callbacks are still in flight, bpf_mem_alloc_destroy() copies the allocator and defers the final drain, together with the destructor context, to a workqueue. bpf_map_free() then frees map->record and drops the map's BTF reference as soon as map_free() returns. Once the program that loaded the BTF is gone as well, the BTF is freed while the worker still uses the duplicate. The worker dereferences it through btf_is_kernel() and btf_find_struct_meta() in bpf_obj_free_fields() when destroying elements that were freed under RCU, and through btf_is_kernel() in btf_record_free() when releasing the context itself: BUG: KASAN: slab-use-after-free in btf_is_kernel+0x19/0x30 Read of size 1 at addr ffff88811505dce8 by task kworker/u16:2/50 Workqueue: events_unbound free_mem_alloc_deferred Call Trace: btf_is_kernel+0x19/0x30 btf_record_free+0xc7/0xf0 htab_dtor_ctx_free+0x1a/0x30 free_mem_alloc_no_barrier+0x39/0x230 free_mem_alloc_deferred+0x2a/0x40 process_scheduled_works+0x5ce/0x9d0 worker_thread+0x42a/0x5e0 kthread+0x1f5/0x230 ret_from_fork+0x1dd/0x390 ret_from_fork_asm+0x1a/0x30 Allocated by task 358: __kmalloc_cache_noprof+0x287/0x510 btf_new_fd+0xf7/0x3d0 __sys_bpf+0x487/0x840 Freed by task 0: kfree+0x186/0x560 rcu_core+0x6f6/0xd40 Freeing a map that still holds more elements than the allocator's high watermark is enough to get there, because the bulk free during teardown queues the RCU callback that makes bpf_mem_alloc_destroy() defer. Non-preallocated hash maps and resizable hash maps both register the destructor and are affected alike. Keep one reference on the map BTF in the destructor context. Every non-kernel pointer in the duplicated record is either map->btf or memory owned by it, so a single reference covers kptrs, list heads, and rb roots, and mirrors what bpf_map_meta_alloc() does for the duplicated record of an inner map. Release it only after the duplicated record has been freed: the worker is preemptible and not in an RCU read-side critical section, so dropping the last reference first would let the BTF be freed while btf_record_free() still reads its fields. | |
| Title | bpf: Hold map BTF for the memory allocator destructor record | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-18T15:48:59.745Z
Reserved: 2026-09-25T10:25:14.371Z
Link: CVE-2026-98813
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-18T16:17:35.427
Modified: 2026-10-18T16:17:35.427
Link: CVE-2026-98813
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.