---
id: "CVE-2026-98789"
kind: "vulnerability"
aliases: ["CVE-2026-98789"]
title: "Linux kernel BPF memory allocator can leak objects indefinitely"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["bpf", "kernel", "linux", "runtime", "self-hosted"]
not_affected_if: ["no-bpf-programs"]
published_at: "2026-10-18T16:17:32+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:15:17+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98789", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux kernel BPF memory allocator can leak objects indefinitely

The BPF memory allocator can leave freed objects stuck in a pending list when an RCU tasks trace grace period is in flight, because the free path returns early and never drains them. The sources describe a resource leak with unbounded growth, not a code execution or data disclosure path.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `uname -r` and compare against the fixed kernel stable release listed in the NVD entry for CVE-2026-98789
- Check whether BPF hash maps are created and destroyed in a loop on the host, which is the pattern the description says triggers the growth

## Fix

- Update the Linux kernel to a stable release that includes the upstream commit 'bpf: Fix objects stuck in free_by_rcu_ttrace' (fixed version unknown from the sources)
- Reboot into the patched kernel after the distribution ships it

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98789

## From the sources

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

bpf: Fix objects stuck in free_by_rcu_ttrace

do_call_rcu_ttrace() returns early when call_rcu_ttrace_in_progress is set
and leaves the objects in free_by_rcu_ttrace. __free_rcu() frees
waiting_for_gp_ttrace only and clears the flag. Hence the objects that
free_bulk() or __free_by_rcu() added while RCU tasks trace GP was in flight
stay in free_by_rcu_ttrace until free_bulk() or alloc_bulk() is called for
the same bpf_mem_cache again, which may never happen. The number of such
objects is not bounded.

Turn call_rcu_ttrace_in_progress into three states:
0 - idle
1 - __free_rcu() is queued
2 - __free_rcu() is queued and free_by_rcu_ttrace got more objects since

do_call_rcu_ttrace() sets 2. __free_rcu() does cmpxchg(1 -> 0) and starts
the next GP when it fails. It cannot clear the flag first and check
free_by_rcu_ttrace later, since bpf_mem_alloc_destroy() frees bpf_mem_cache
without waiting for RCU callbacks when the flag is zero.

Now __free_rcu() queues itself, so the one that didn't see 'draining' may
do call_rcu_tasks_trace() after rcu_barrier_tasks_trace() in
free_mem_alloc(). Queue it under rcu_read_lock() and do synchronize_rcu()
before the barriers. Calling rcu_barrier_tasks_trace() twice works too, but
creating and destroying hash maps in a loop on many cpus slows down to one
free_mem_alloc() per GP and kworkers pile up.

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