# CVE-2026-89902: LoongArch: Avoid preempt count underflow without probe

CVE-2026-89902 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-89902, released September 23, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-89902
- Priority: High
- CVSS: 7.8 (Important)
- EPSS: 0.0018
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 16, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-89902

## Description

In the Linux kernel, the following vulnerability has been resolved:  LoongArch: Avoid preempt count underflow without probe  LoongArch uses break 11 for the breakpoint placed after an instruction that Kprobes executes out of line. Since userspace can issue the same break instruction, do_bp() can reach kprobe_singlestep_handler() when there is no current probe.  The handler actually returns false in this case, but it first calls preempt_enable_no_resched(). The corresponding preempt_disable() is done by kprobe_breakpoint_handler() on a real Kprobe hit, so it has not run here. As a result, an ordinary userspace breakpoint (code 11) underflows the current task's preempt count.  This also makes in_interrupt() return true until the task schedules. One visible consequence is the socket cgroup attribution: cgroup_sk_alloc() treats the allocation as interrupt context and assigns the socket to the root cgroup. A socket opened from the SIGTRAP handler can then avoid a BPF_CGROUP_INET_SOCK_CREATE policy attached to the task's own cgroup.  Return as soon as kprobe_running() reports no active probe.  The same check has appeared in [PATCH v10 2/4] of the original LoongArch Kprobes series, but was dropped before the feature reached mainline.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.111-1 | [DEBIAN-CVE-2026-89902](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89902.md) | Sep 23, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-89902](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89902.md) | Sep 23, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.111-1~deb12u1 | [DEBIAN-CVE-2026-89902](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89902.md) | Sep 23, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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