# CVE-2024-35929: linux: In the Linux kernel, the following vulnerability has been resolved:  rcu/nocb: Fix WARN_ON_ONCE() in the rcu_nocb_byp...

CVE-2024-35929 is fixed in linux on 1 platform, first by DEBIAN-CVE-2024-35929, released May 19, 2024. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2024-35929
- Priority: High
- CVSS: 7.8 (high)
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 19, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  rcu/nocb: Fix WARN_ON_ONCE() in the rcu_nocb_bypass_lock()  For the kernels built with CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y and CONFIG_RCU_LAZY=y, the following scenarios will trigger WARN_ON_ONCE() in the rcu_nocb_bypass_lock() and rcu_nocb_wait_contended() functions:          CPU2                                               CPU11 kthread rcu_nocb_cb_kthread                                       ksys_write rcu_do_batch                                              vfs_write rcu_torture_timer_cb                                      proc_sys_write __kmem_cache_free                                         proc_sys_call_handler kmemleak_free                                             drop_caches_sysctl_handler delete_object_full                                        drop_slab __delete_object                                           shrink_slab put_object                                                lazy_rcu_shrink_scan call_rcu                                                  rcu_nocb_flush_bypass __call_rcu_commn                                            rcu_nocb_bypass_lock                                                             raw_spin_trylock(&rdp->nocb_bypass_lock) fail                                                             atomic_inc(&rdp->nocb_lock_contended); rcu_nocb_wait_contended                                     WARN_ON_ONCE(smp_processor_id() != rdp->cpu);  WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended))                                          |                             |_ _ _ _ _ _ _ _ _ _same rdp and rdp->cpu != 11_ _ _ _ _ _ _ _ _ __|  Reproduce this bug with "echo 3 > /proc/sys/vm/drop_caches".  This commit therefore uses rcu_nocb_try_flush_bypass() instead of rcu_nocb_flush_bypass() in lazy_rcu_shrink_scan().  If the nocb_bypass queue is being flushed, then rcu_nocb_try_flush_bypass will return directly.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.8.9-1 | [DEBIAN-CVE-2024-35929](https://patchblox.com/security/data/fix/linux/debian-cve-2024-35929.md) | May 19, 2024 |
| Linux | linux Debian 14 | 6.8.9-1 | [DEBIAN-CVE-2024-35929](https://patchblox.com/security/data/fix/linux/debian-cve-2024-35929.md) | May 19, 2024 |

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