CVE-2021-47512

/// Technical 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]

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References