The Linux kernel vulnerability (CVE-2026-89580) concerns the BPF subsystem's __bpf_get_stack function. The get_perf_callchain() function returns a per-CPU perf_callchain_entry buffer and releases its recursion slot before returning, which allows a preemptible BPF program to be scheduled out between obtaining and copying the entry. This scheduling out permits another task on the same CPU to reuse and overwrite the buffer, inflating trace->nr and causing an out-of-bounds write during memcpy and build_id resolution. The existing rcu_read_lock() does not prevent this race under CONFIG_PREEMPT_RCU. The fix involves disabling preemption during the critical section to ensure the buffer is not reused and trace->nr remains bounded, deferring build ID resolution until after preemption is re-enabled.

This vulnerability can lead to out-of-bounds memory writes in the kernel, which may cause memory corruption, system instability, or potential escalation of privileges if exploited. However, no known exploits in the wild have been reported.

A fix has been implemented that disables preemption around obtaining and copying the callchain entry to prevent buffer reuse and out-of-bounds writes. Users should apply the official Linux kernel updates that include this fix once available. Patch status is not explicitly confirmed in the provided data; therefore, check the vendor advisory for current remediation guidance.