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CVE-2026-89500
ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem kernel/trace. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89500 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixedDSA-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| 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
Discarding a cached reader page after a concurrent ring buffer resize uses the new global subbuf_order for the free_pages() call. This mismatched order may crashes the kernel or leaks memory because the cached page was allocated under the old size. Save the actual free_page order alongside the page address to ensure we always refer to the correct value and do not rely on the potentially stalled cpu_buffer->subbuf_order value. The simplest is to make free_page a buffer_data_read_page which already covers exactly what we need: a page address and a page order.
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.
kernel/trace/ring_buffer.c
- What this is
- TRACINGMAINTAINERS section matched on kernel/trace/ · linux-kernel@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_FUNCTION_TRACER|CONFIG_RETHOOK|CONFIG_RING_BUFFER|CONFIG_TRACEPOINTS|CONFIG_TRACE_CLOCK|CONFIG_TRACING' /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.
- bookwormYnot built on arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
- trixieYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- forky, sidYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae
- Y
- built in where it is built at all; some flavours do not build it
- Build switches
- CONFIG_FUNCTION_TRACER, CONFIG_RETHOOK, CONFIG_RING_BUFFER, CONFIG_TRACEPOINTS, CONFIG_TRACE_CLOCK, CONFIG_TRACING
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-09-11 (37 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
- 0.16%, higher than 5.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- kernel/trace
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.8 | 6.12.112 | d8f52dc3c3f1 |
| 6.8 | 6.18.51 | a1dabe68fb53 |
| 6.8 | 7.2.4 | d787d509bdf6 |
| 6.8 | 7.3 | 7a1fb95de540 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | tracker |
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 reached only via local tracefs: write() to buffer_subbuf_size_kb (buffer_subbuf_size_write -> ring_buffer_subbuf_order_set) racing read/splice/close of per_cpu/cpuN/trace_pipe_raw (ring_buffer_alloc_read_page / ring_buffer_free_read_page) or instance rmdir (rb_free_cpu_buffer). No network, adjacent-radio, or physical path exists.
- AC:LAttack complexity, low
- The attacker owns both sides of the race: one thread toggles buffer_subbuf_size_kb while another caches or discards a reader page via trace_pipe_raw. The window includes synchronize_rcu() and GFP_KERNEL allocation of every new sub-buffer, so the mismatch is reliably retryable with no condition outside attacker control.
- PR:LPrivileges required, low
- tracing_check_open_get_tr() enforces only LOCKDOWN_TRACEFS and DAC, with no capable() check. buffer_subbuf_size_kb is 0640 and trace_pipe_raw is 0440; Android/Perfetto, ChromeOS, and distro tracing groups routinely delegate these to unprivileged accounts, matching CVE-2024-50207, CVE-2025-38101, and CVE-2026-74634.
- UI:NUser interaction, none
- Exploitation uses the attacker's own file descriptors and threads (write buffer_subbuf_size_kb, read/close trace_pipe_raw, optional instance rmdir). No separate victim mount, click, or configuration action is required.
- S:UScope, unchanged
- Wrong-order free_pages() and reuse of a cached reader page corrupt kernel ring-buffer and buddy-allocator pages within the same OS security authority. This enables local privilege escalation but does not cross VM, IOMMU, container, or hardware trust boundaries.
- C:HConfidentiality impact, high
- cpu_buffer->free_page stored no allocation order, so a cached page allocated under the old subbuf size can be discarded or reused with the new order. Over-free and undersized-page swap are page UAF/OOB reads; recycled buddy pages and ring-buffer contents can be disclosed through subsequent trace_pipe_raw reads.
- I:HIntegrity impact, high
- free_pages() with a larger-than-allocated order returns neighboring in-use pages to the buddy allocator (page UAF/write). ring_buffer_read_page() can also swap that undersized cached page into the live writer path, producing out-of-bounds kernel stores exploitable for control-flow hijack.
- A:HAvailability impact, high
- Mismatched-order free_pages() corrupts the buddy allocator and the commit states this may crash the kernel; UAF/OOB on ring-buffer pages also oops/panic. The attacker chooses the order delta via buffer_subbuf_size_kb and can retrigger the race at will.