CVE-2024-35929 Affecting kernel-debug package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-debug package and not the kernel-debug package as distributed by RHEL. See How to fix? for RHEL:8 relevant fixed versions and status.

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.

• https://access.redhat.com/security/cve/CVE-2024-35929
• https://git.kernel.org/stable/c/4d58c9fb45c70e62c19e8be3f3605889c47601bc
• https://git.kernel.org/stable/c/927d1f4f77e4784ab3944a9df86ab14d1cd3185a
• https://git.kernel.org/stable/c/dda98810b552fc6bf650f4270edeebdc2f28bd3f