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CVE-2026-89906
LoongArch: BPF: Refactor jump offset calculation in tail call
Published 2026-09-16 (33 days ago) by the Linux kernel CNA. Subsystem arch/loongarch. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89906 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The old macro-based jmp_offset calculation derives the jump distance from a stale prior-pass code stride, which can lead to wrong branch offsets and soft lockups under extra JIT passes. Fix this by calculating the offset directly on the absolute target: "ctx->offset[insn + 1] - ctx->idx". To avoid a false 16-bit range check abort during size estimation, add a "ctx->image == NULL" guard to inject a safe dummy offset.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
arch/loongarch/net/bpf_jit.c
- What this is
- BPF JIT for LOONGARCHMAINTAINERS section matched on arch/loongarch/net/ · bpf@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_BPF_JIT /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormy
- trixie, forky, sidYnot built on s390x/s390x
- y
- built into the kernel image on every flavour - only a patch removes it
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_BPF_JIT
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-16 (33 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- arch/loongarch
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.17 | 6.18.51 | 882b8912b7e9 |
| 6.17 | 7.2.5 | 96f44d493c28 |
| 6.17 | 7.3 | 37d545d12f21 |
| 6.1.149 | 0 | 0 |
| 6.6.103 | 0 | 0 |
| 6.12.43 | 0 | 0 |
| 6.15.11 | 0 | 0 |
| 6.16.2 | 0 | 0 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is in the LoongArch eBPF JIT emit_bpf_tail_call() and is reached only by loading a program that uses bpf_tail_call via bpf(BPF_PROG_LOAD) on the local host. Kernel CNA guidance classifies BPF as a local attack vector.
- AC:LAttack complexity, low
- The attacker fully controls the BPF bytecode, including bpf2bpf subprograms that force the extra JIT pass where the stale prior-pass stride is used. Wrong jmp_offset encodings are deterministic for a given program (the in-tree tailcall_bpf2bpf_1 case), with no race or layout outside attacker control.
- PR:LPrivileges required, low
- BPF_MAP_TYPE_PROG_ARRAY is an unprivileged map type, bpf_tail_call_proto is returned before the CAP_BPF gate, and SOCKET_FILTER programs load without CAP_BPF where unprivileged BPF is enabled. Otherwise only CAP_BPF or a delegated BPF token in a user namespace is required, not init-namespace root.
- UI:NUser interaction, none
- The attacker loads the crafted program, attaches it to a socket they own or runs it with BPF_PROG_TEST_RUN, and triggers the miscompiled tail call themselves. No separate victim action is required.
- S:UScope, unchanged
- The wrong branches execute inside the host kernel's own JIT image and corrupt in-kernel control flow. That is standard kernel privilege-escalation impact, not a VM, IOMMU, or hypervisor boundary crossing.
- C:HConfidentiality impact, high
- Miscomputed tail-call "goto out" branches can land inside the remaining sequence after the max_entries check, so an out-of-range index performs an OOB load of array->ptrs[] and treats the result as a function pointer, disclosing kernel memory. Mid-image jumps likewise execute attacker-shaped JIT loads at kernel privilege.
- I:HIntegrity impact, high
- The same OOB ptrs[] load is followed by an indirect jump through prog->bpf_func, hijacking kernel control flow. Branches that skip the NULL or tail-call-count checks, or that land mid-instruction, likewise yield a kernel-mode write and control-flow primitive.
- A:HAvailability impact, high
- The fix and the prior incomplete tail-call offset patch document watchdog soft lockups from wrong, including backward, branches looping in kernel context. Any such hang, oops, or panic is Availability High.