In the Linux kernel, the following vulnerability has been resolved:
bpf: Harden bloom filter sizing and indexing on 32-bit kernels
bloom_map_alloc() has two 32-bit-specific problems when the computed
bitmap reaches the U32_MAX fallback case.
First, BITS_TO_BYTES(U32_MAX) is evaluated with 32-bit arithmetic. The
addition performed by DIV_ROUND_UP wraps, so the map allocates only the
fixed-size bloom filter object while keeping bitset_mask == U32_MAX.
Subsequent updates can then write past the allocated object.
Second, fixing only the allocation size is not sufficient. The bloom hash
is a u32, but set_bit() takes a signed long bit number and x86 test_bit()
eventually feeds the index to variable_test_bit(long, ...). On 32-bit
kernels, hashes in [0x80000000, U32_MAX] therefore become negative bit
offsets. x86 bt/bts with a memory operand interpret those offsets relative
to the supplied base, so a map with bitset_mask == U32_MAX can read or
write before bloom->bitset even after allocating the full 512 MiB bitmap.
Keep the U32_MAX fallback, but split each hash into a word pointer and an
in-word bit number before calling test_bit() or set_bit(). The bitops
argument is then always in [0, BITS_PER_LONG - 1], while BIT_WORD(h) still
selects the intended word in the full bitmap.
Compute the bitset size from (u64)bitset_mask + 1 before passing the final
size to bpf_map_area_alloc(). This fixes the original under-allocation and
keeps the allocated storage consistent with the addressable bitset.
Exploitation note: local privilege escalation is possible on a 32-bit x86
kernel using the under-allocation bug from a binary with CAP_BPF.
bpf: Harden bloom filter sizing and indexing on 32-bit kernels
bloom_map_alloc() has two 32-bit-specific problems when the computed
bitmap reaches the U32_MAX fallback case.
First, BITS_TO_BYTES(U32_MAX) is evaluated with 32-bit arithmetic. The
addition performed by DIV_ROUND_UP wraps, so the map allocates only the
fixed-size bloom filter object while keeping bitset_mask == U32_MAX.
Subsequent updates can then write past the allocated object.
Second, fixing only the allocation size is not sufficient. The bloom hash
is a u32, but set_bit() takes a signed long bit number and x86 test_bit()
eventually feeds the index to variable_test_bit(long, ...). On 32-bit
kernels, hashes in [0x80000000, U32_MAX] therefore become negative bit
offsets. x86 bt/bts with a memory operand interpret those offsets relative
to the supplied base, so a map with bitset_mask == U32_MAX can read or
write before bloom->bitset even after allocating the full 512 MiB bitmap.
Keep the U32_MAX fallback, but split each hash into a word pointer and an
in-word bit number before calling test_bit() or set_bit(). The bitops
argument is then always in [0, BITS_PER_LONG - 1], while BIT_WORD(h) still
selects the intended word in the full bitmap.
Compute the bitset size from (u64)bitset_mask + 1 before passing the final
size to bpf_map_area_alloc(). This fixes the original under-allocation and
keeps the allocated storage consistent with the addressable bitset.
Exploitation note: local privilege escalation is possible on a 32-bit x86
kernel using the under-allocation bug from a binary with CAP_BPF.
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 |
|
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| Linux | Linux | affected |
|
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Advisories
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Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Fri, 11 Sep 2026 23:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: bpf: Harden bloom filter sizing and indexing on 32-bit kernels bloom_map_alloc() has two 32-bit-specific problems when the computed bitmap reaches the U32_MAX fallback case. First, BITS_TO_BYTES(U32_MAX) is evaluated with 32-bit arithmetic. The addition performed by DIV_ROUND_UP wraps, so the map allocates only the fixed-size bloom filter object while keeping bitset_mask == U32_MAX. Subsequent updates can then write past the allocated object. Second, fixing only the allocation size is not sufficient. The bloom hash is a u32, but set_bit() takes a signed long bit number and x86 test_bit() eventually feeds the index to variable_test_bit(long, ...). On 32-bit kernels, hashes in [0x80000000, U32_MAX] therefore become negative bit offsets. x86 bt/bts with a memory operand interpret those offsets relative to the supplied base, so a map with bitset_mask == U32_MAX can read or write before bloom->bitset even after allocating the full 512 MiB bitmap. Keep the U32_MAX fallback, but split each hash into a word pointer and an in-word bit number before calling test_bit() or set_bit(). The bitops argument is then always in [0, BITS_PER_LONG - 1], while BIT_WORD(h) still selects the intended word in the full bitmap. Compute the bitset size from (u64)bitset_mask + 1 before passing the final size to bpf_map_area_alloc(). This fixes the original under-allocation and keeps the allocated storage consistent with the addressable bitset. Exploitation note: local privilege escalation is possible on a 32-bit x86 kernel using the under-allocation bug from a binary with CAP_BPF. | |
| Title | bpf: Harden bloom filter sizing and indexing on 32-bit kernels | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-11T19:44:46.110Z
Reserved: 2026-09-11T19:38:34.728Z
Link: CVE-2026-89579
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-11T20:19:42.127
Modified: 2026-09-11T20:19:42.127
Link: CVE-2026-89579
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.