{
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"cveMetadata": {
"cveId": "CVE-2021-47512",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2024-05-24T15:02:54.824Z",
"datePublished": "2024-05-24T15:09:27.356Z",
"dateUpdated": "2026-08-05T08:48:11.315Z"
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_pie: prevent dismantle issue\n\nFor some reason, fq_pie_destroy() did not copy\nworking code from pie_destroy() and other qdiscs,\nthus causing elusive bug.\n\nBefore calling del_timer_sync(&q->adapt_timer),\nwe need to ensure timer will not rearm itself.\n\nrcu: INFO: rcu_preempt self-detected stall on CPU\nrcu: 0-....: (4416 ticks this GP) idle=60d/1/0x4000000000000000 softirq=10433/10434 fqs=2579\n (t=10501 jiffies g=13085 q=3989)\nNMI backtrace for cpu 0\nCPU: 0 PID: 13 Comm: ksoftirqd/0 Not tainted 5.16.0-rc4-syzkaller #0\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011\nCall Trace:\n \n __dump_stack lib/dump_stack.c:88 [inline]\n dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106\n nmi_cpu_backtrace.cold+0x47/0x144 lib/nmi_backtrace.c:111\n nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62\n trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]\n rcu_dump_cpu_stacks+0x25e/0x3f0 kernel/rcu/tree_stall.h:343\n print_cpu_stall kernel/rcu/tree_stall.h:627 [inline]\n check_cpu_stall kernel/rcu/tree_stall.h:711 [inline]\n rcu_pending kernel/rcu/tree.c:3878 [inline]\n rcu_sched_clock_irq.cold+0x9d/0x746 kernel/rcu/tree.c:2597\n update_process_times+0x16d/0x200 kernel/time/timer.c:1785\n tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226\n tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1428\n __run_hrtimer kernel/time/hrtimer.c:1685 [inline]\n __hrtimer_run_queues+0x1c0/0xe50 kernel/time/hrtimer.c:1749\n hrtimer_interrupt+0x31c/0x790 kernel/time/hrtimer.c:1811\n local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]\n __sysvec_apic_timer_interrupt+0x146/0x530 arch/x86/kernel/apic/apic.c:1103\n sysvec_apic_timer_interrupt+0x8e/0xc0 arch/x86/kernel/apic/apic.c:1097\n \n \n asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638\nRIP: 0010:write_comp_data kernel/kcov.c:221 [inline]\nRIP: 0010:__sanitizer_cov_trace_const_cmp1+0x1d/0x80 kernel/kcov.c:273\nCode: 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 4e f7 ff ff 84 c0 74 51 48 8b 81 88 15 00 00 44 8b 81 84 15 00\nRSP: 0018:ffffc90000d27b28 EFLAGS: 00000246\nRAX: 0000000000000000 RBX: ffff888064bf1bf0 RCX: ffff888011928000\nRDX: ffff888011928000 RSI: ffff888011928000 RDI: 0000000000000003\nRBP: ffff888064bf1c28 R08: 0000000000000000 R09: 0000000000000000\nR10: ffffffff875d8295 R11: 0000000000000000 R12: 0000000000000000\nR13: ffff8880783dd300 R14: 0000000000000000 R15: 0000000000000000\n pie_calculate_probability+0x405/0x7c0 net/sched/sch_pie.c:418\n fq_pie_timer+0x170/0x2a0 net/sched/sch_fq_pie.c:383\n call_timer_fn+0x1a5/0x6b0 kernel/time/timer.c:1421\n expire_timers kernel/time/timer.c:1466 [inline]\n __run_timers.part.0+0x675/0xa20 kernel/time/timer.c:1734\n __run_timers kernel/time/timer.c:1715 [inline]\n run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1747\n __do_softirq+0x29b/0x9c2 kernel/softirq.c:558\n run_ksoftirqd kernel/softirq.c:921 [inline]\n run_ksoftirqd+0x2d/0x60 kernel/softirq.c:913\n smpboot_thread_fn+0x645/0x9c0 kernel/smpboot.c:164\n kthread+0x405/0x4f0 kernel/kthread.c:327\n ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295\n "
}
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"version": "3.1",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"baseScore": 7.8,
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"value": "AV:L - The bug is triggered by creating and destroying an fq_pie qdisc through RTM_NEWQDISC/RTM_DELQDISC rtnetlink (tc), which requires a local netlink socket; no remote peer input reaches fq_pie_destroy or the adapt_timer path.\nAC:L - The attacker controls both sides of the race—arming the self-rearming adapt_timer by installing fq_pie (and can set a short tupdate) then deleting the qdisc to enter fq_pie_destroy—and can retry the create/destroy sequence until the timer runs across the missing tupdate=0 teardown window.\nPR:L - Qdisc configuration is gated only by netlink_net_capable(skb, CAP_NET_ADMIN) against the netns user_ns, so an unprivileged user obtains the needed capability via unshare -Urn and can attach fq_pie on lo; sch_fq_pie is also request_module-autoloadable from that path.\nUI:N - The attacker performs the entire sequence—namespace setup, qdisc create, and qdisc delete—without any action by another user.\nS:U - The timer/UAF and any resulting memory corruption stay inside the host kernel’s own net/sched authority; this is standard local kernel impact with no VM, IOMMU, or sandbox boundary crossed.\nC:H - Without zeroing tupdate before del_timer_sync, the self-rearming timer can still run after teardown while kvfree(q->flows) has already freed the flow table, yielding a use-after-free read over reclaimable kernel heap that can disclose arbitrary kernel memory.\nI:H - The same post-dismantle UAF on the flows array (and related fq_pie_sched_data state) allows heap reuse and attacker-controlled corruption of kernel objects, matching the net/sched local privilege-escalation pattern for timer-vs-teardown use-after-frees.\nA:H - The observed failure is an RCU self-detected stall / hang in fq_pie_timer, and a use-after-free on freed flows also produces kernel oops/panic; either outcome is a complete availability loss."
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"timestamp": "2024-06-17T17:36:33.443173Z",
"id": "CVE-2021-47512",
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