CVE-2021-47512 (Moderate severity, published 2024-05-23)
CVSS score: 4.4 (CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H)
CWE: CWE-414
Description: In the Linux kernel, the following vulnerability has been resolved:

net/sched: fq_pie: prevent dismantle issue

For some reason, fq_pie_destroy() did not copy
working code from pie_destroy() and other qdiscs,
thus causing elusive bug.

Before calling del_timer_sync(&q->adapt_timer),
we need to ensure timer will not rearm itself.

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu:    0-....: (4416 ticks this GP) idle=60d/1/0x4000000000000000 softirq=10433/10434 fqs=2579
        (t=10501 jiffies g=13085 q=3989)
NMI backtrace for cpu 0
CPU: 0 PID: 13 Comm: ksoftirqd/0 Not tainted 5.16.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 nmi_cpu_backtrace.cold+0x47/0x144 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x25e/0x3f0 kernel/rcu/tree_stall.h:343
 print_cpu_stall kernel/rcu/tree_stall.h:627 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:711 [inline]
 rcu_pending kernel/rcu/tree.c:3878 [inline]
 rcu_sched_clock_irq.cold+0x9d/0x746 kernel/rcu/tree.c:2597
 update_process_times+0x16d/0x200 kernel/time/timer.c:1785
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226
 tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1428
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x1c0/0xe50 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x31c/0x790 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]
 __sysvec_apic_timer_interrupt+0x146/0x530 arch/x86/kernel/apic/apic.c:1103
 sysvec_apic_timer_interrupt+0x8e/0xc0 arch/x86/kernel/apic/apic.c:1097
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
RIP: 0010:write_comp_data kernel/kcov.c:221 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp1+0x1d/0x80 kernel/kcov.c:273
Code: 54 c8 20 48 89 10 c3 66 0f 1f 44 00 00 53 41 89 fb 41 89 f1 bf 03 00 00 00 65 48 8b 0c 25 40 70 02 00 48 89 ce 4c 8b 54 24 08 <e8> 4e f7 ff ff 84 c0 74 51 48 8b 81 88 15 00 00 44 8b 81 84 15 00
RSP: 0018:ffffc90000d27b28 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff888064bf1bf0 RCX: ffff888011928000
RDX: ffff888011928000 RSI: ffff888011928000 RDI: 0000000000000003
RBP: ffff888064bf1c28 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff875d8295 R11: 0000000000000000 R12: 0000000000000000
R13: ffff8880783dd300 R14: 0000000000000000 R15: 0000000000000000
 pie_calculate_probability+0x405/0x7c0 net/sched/sch_pie.c:418
 fq_pie_timer+0x170/0x2a0 net/sched/sch_fq_pie.c:383
 call_timer_fn+0x1a5/0x6b0 kernel/time/timer.c:1421
 expire_timers kernel/time/timer.c:1466 [inline]
 __run_timers.part.0+0x675/0xa20 kernel/time/timer.c:1734
 __run_timers kernel/time/timer.c:1715 [inline]
 run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1747
 __do_softirq+0x29b/0x9c2 kernel/softirq.c:558
 run_ksoftirqd kernel/softirq.c:921 [inline]
 run_ksoftirqd+0x2d/0x60 kernel/softirq.c:913
 smpboot_thread_fn+0x645/0x9c0 kernel/smpboot.c:164
 kthread+0x405/0x4f0 kernel/kthread.c:327
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
Statement: Red Hat Enterprise Linux is not impacted by this CVE, as the vulnerability in question does not affect the specific versions or configurations of the Linux kernel used in its distributions. This ensures that users of Red Hat Enterprise Linux are not exposed to the potential risks associated with this issue, and no further action or mitigation is necessary for systems running this operating system.
Mitigation: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.