# CVE-2021-47512: linux: In the Linux kernel, the following vulnerability has been resolved:  net/sched: fq_pie: prevent dismantle issue  For...

CVE-2021-47512 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47512, released May 24, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47512
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0025
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 24, 2024

## 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>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.15-1 | [DEBIAN-CVE-2021-47512](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47512.md) | May 24, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.15-1 | [DEBIAN-CVE-2021-47512](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47512.md) | May 24, 2024 |
| Linux | linux Debian 14 | 5.15.15-1 | [DEBIAN-CVE-2021-47512](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47512.md) | May 24, 2024 |

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