CVE-2026-89902
HighCVSS 7.8Summary
In the Linux kernel for LoongArch, there is a vulnerability related to break 11 handling in the context of Kprobes. A user can issue the same break instruction, causing kprobe_singlestep_handler() to be called without an active probe, leading to preempt count underflow. This may result in incorrect socket attribution to the root cgroup, bypassing BPF policies.
Risk Assessment
The vulnerability may allow bypassing BPF security policies (e.g., BPF_CGROUP_INET_SOCK_CREATE) by assigning sockets to the root cgroup, potentially leading to unauthorized network traffic or privilege escalation.
Recommendation
Apply the kernel patch that adds an early return when no active probe is present and update to a kernel version containing the fix.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS