CVE-2026-23159

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

perf: sched: Fix perf crash with new is_user_task() helper

In order to do a user space stacktrace the current task needs to be a user

task that has executed in user space. It use to be possible to test if a

task is a user task or not by simply checking the task_struct mm field. If

it was non NULL, it was a user task and if not it was a kernel task.

But things have changed over time, and some kernel tasks now have their

own mm field.

An idea was made to instead test PF_KTHREAD and two functions were used to

wrap this check in case it became more complex to test if a task was a

user task or not[1]. But this was rejected and the C code simply checked

the PF_KTHREAD directly.

It was later found that not all kernel threads set PF_KTHREAD. The io-uring

helpers instead set PF_USER_WORKER and this needed to be added as well.

But checking the flags is still not enough. There's a very small window

when a task exits that it

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References