[Linux kernel bug] WARNING in free_event

From: Sam Sun
Date: Wed Apr 17 2024 - 09:40:48 EST

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Dear developers and maintainers,

We encountered a kernel warning in the function free_event() while
using our modified syzkaller. It was tested on the latest upstream
linux(6.9-rc4). C repro and kernel config are attached to this email.
Kernel dump log is listed below.
```

------------[ cut here ]------------
unexpected event refcount: 2; ptr=ffff88801931e0c0
WARNING: CPU: 0 PID: 8082 at kernel/events/core.c:5254
free_event+0xa3/0xc0 kernel/events/core.c:5254
Modules linked in:
CPU: 0 PID: 8082 Comm: syz-executor381 Not tainted 6.7.0-rc7 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:free_event+0xa3/0xc0 kernel/events/core.c:5254
Code: b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 75 25 48 8b
b5 38 02 00 00 48 89 ea 48 c7 c7 c0 38 b7 8a e8 6e 30 9e ff 90 <0f> 0b
90 90 5d 41 5c 41 5d e9 bf 45 d7 ff 4c 89 ef e8 d7 e9 2b 00
RSP: 0018:ffffc9000176f9e8 EFLAGS: 00010282
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff814c00fa
RDX: ffff888063d919c0 RSI: ffffffff814c0107 RDI: 0000000000000001
RBP: ffff88801931e0c0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000002
R13: ffff88801931e2f8 R14: ffff88801931e3a0 R15: ffff88801931e0c0
FS: 0000000000000000(0000) GS:ffff888044200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000008 CR3: 000000000cd78000 CR4: 0000000000750ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
perf_event_release_kernel+0x5d4/0x8f0 kernel/events/core.c:5421
perf_release+0x37/0x50 kernel/events/core.c:5442
__fput+0x282/0xbb0 fs/file_table.c:394
task_work_run+0x168/0x260 kernel/task_work.c:180
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xaf0/0x2a40 kernel/exit.c:869
do_group_exit+0xd4/0x2a0 kernel/exit.c:1018
get_signal+0x243c/0x2630 kernel/signal.c:2904
arch_do_signal_or_restart+0x81/0x7d0 arch/x86/kernel/signal.c:309
exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
exit_to_user_mode_prepare+0x121/0x240 kernel/entry/common.c:204
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x1e/0x60 kernel/entry/common.c:296
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
</TASK>
```
If you have any questions, please contact us.
Reported by: Yue Sun <samsun1006219@xxxxxxxxx>
Reported by: xingwei lee <xrivendell7@xxxxxxxxx>

Best Regards,
Yue

Attachment: config
Description: Binary data

#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

static void sleep_ms(uint64_t ms)
{
usleep(ms * 1000);
}

static uint64_t current_time_ms(void)
{
struct timespec ts;
if (clock_gettime(CLOCK_MONOTONIC, &ts))
exit(1);
return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}

#define BITMASK(bf_off, bf_len) (((1ull << (bf_len)) - 1) << (bf_off))
#define STORE_BY_BITMASK(type, htobe, addr, val, bf_off, bf_len) \
*(type*)(addr) = \
htobe((htobe(*(type*)(addr)) & ~BITMASK((bf_off), (bf_len))) | \
(((type)(val) << (bf_off)) & BITMASK((bf_off), (bf_len))))

static bool write_file(const char* file, const char* what, ...)
{
char buf[1024];
va_list args;
va_start(args, what);
vsnprintf(buf, sizeof(buf), what, args);
va_end(args);
buf[sizeof(buf) - 1] = 0;
int len = strlen(buf);
int fd = open(file, O_WRONLY | O_CLOEXEC);
if (fd == -1)
return false;
if (write(fd, buf, len) != len) {
int err = errno;
close(fd);
errno = err;
return false;
}
close(fd);
return true;
}

static void kill_and_wait(int pid, int* status)
{
kill(-pid, SIGKILL);
kill(pid, SIGKILL);
for (int i = 0; i < 100; i++) {
if (waitpid(-1, status, WNOHANG | __WALL) == pid)
return;
usleep(1000);
}
DIR* dir = opendir("/sys/fs/fuse/connections");
if (dir) {
for (;;) {
struct dirent* ent = readdir(dir);
if (!ent)
break;
if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
continue;
char abort[300];
snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort",
ent->d_name);
int fd = open(abort, O_WRONLY);
if (fd == -1) {
continue;
}
if (write(fd, abort, 1) < 0) {
}
close(fd);
}
closedir(dir);
} else {
}
while (waitpid(-1, status, __WALL) != pid) {
}
}

static void setup_test()
{
prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
setpgrp();
write_file("/proc/self/oom_score_adj", "1000");
}

#define USLEEP_FORKED_CHILD (3 * 50 * 1000)

static long handle_clone_ret(long ret)
{
if (ret != 0) {
return ret;
}
usleep(USLEEP_FORKED_CHILD);
syscall(__NR_exit, 0);
while (1) {
}
}

static long syz_clone(volatile long flags, volatile long stack,
volatile long stack_len, volatile long ptid,
volatile long ctid, volatile long tls)
{
long sp = (stack + stack_len) & ~15;
long ret = (long)syscall(__NR_clone, flags & ~CLONE_VM, sp, ptid, ctid, tls);
return handle_clone_ret(ret);
}

static void execute_one(void);

#define WAIT_FLAGS __WALL

static void loop(void)
{
int iter = 0;
for (;; iter++) {
int pid = fork();
if (pid < 0)
exit(1);
if (pid == 0) {
setup_test();
execute_one();
exit(0);
}
int status = 0;
uint64_t start = current_time_ms();
for (;;) {
if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid)
break;
sleep_ms(1);
if (current_time_ms() - start < 5000)
continue;
kill_and_wait(pid, &status);
break;
}
}
}

void execute_one(void)
{
*(uint32_t*)0x20000000 = 0;
*(uint32_t*)0x20000004 = 0x80;
*(uint8_t*)0x20000008 = 0;
*(uint8_t*)0x20000009 = 0;
*(uint8_t*)0x2000000a = 0;
*(uint8_t*)0x2000000b = 0;
*(uint32_t*)0x2000000c = 0;
*(uint64_t*)0x20000010 = 0x40000;
*(uint64_t*)0x20000018 = 0;
*(uint64_t*)0x20000020 = 0;
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 0, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 1, 1, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 2, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 3, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 4, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 5, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 6, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 7, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 8, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 9, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 10, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 11, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 12, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 13, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 14, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 15, 2);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 17, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 18, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 19, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 20, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 21, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 22, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 23, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 24, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 25, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 26, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 27, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 28, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 29, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 30, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 31, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 32, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 33, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 34, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 35, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 1, 36, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 1, 37, 1);
STORE_BY_BITMASK(uint64_t, , 0x20000028, 0, 38, 26);
*(uint32_t*)0x20000030 = 0;
*(uint32_t*)0x20000034 = 0;
*(uint64_t*)0x20000038 = 0x100000000000000;
*(uint64_t*)0x20000040 = 0;
*(uint64_t*)0x20000048 = 0;
*(uint64_t*)0x20000050 = 0;
*(uint32_t*)0x20000058 = 0;
*(uint32_t*)0x2000005c = 0;
*(uint64_t*)0x20000060 = 0;
*(uint32_t*)0x20000068 = 0;
*(uint16_t*)0x2000006c = 0;
*(uint16_t*)0x2000006e = 0;
*(uint32_t*)0x20000070 = 0;
*(uint32_t*)0x20000074 = 0;
*(uint64_t*)0x20000078 = 0;
syscall(__NR_perf_event_open, /*attr=*/0x20000000ul, /*pid=*/0, /*cpu=*/0ul,
/*group=*/-1, /*flags=*/0ul);
syz_clone(/*flags=*/0, /*stack=*/0, /*stack_len=*/0, /*parentid=*/0,
/*childtid=*/0, /*tls=*/0);
}
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul,
/*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/ 7ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
loop();
return 0;
}

Next message: Greg KH: "Re: Please create the email alias do-not-apply-to-stable@xxxxxxxxxx -> /dev/null"
Previous message: Georgi Djakov: "[PATCH v8 2/7] iommu/arm-smmu-qcom-debug: Add support for TBUs"
Next in thread: Ian Rogers: "Re: [Linux kernel bug] WARNING in free_event"
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