[Linux kernel bug] WARNING in ax25_dev_device_down

[Sam Sun]

Dear developers and maintainers,

We encountered a kernel warning in function ax25_dev_device_down
during testing using our modified syzkaller. It is tested against the
latest upstream linux (6.9-rc3). C repro and kernel config are
attached to this email. Kernel log is listed below.
```
WARNING: CPU: 0 PID: 8121 at lib/ref_tracker.c:255
ref_tracker_free+0x610/0x830 lib/ref_tracker.c:255
Modules linked in:
CPU: 0 PID: 8121 Comm: syz-executor329 Not tainted 6.7.0-rc7 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:ref_tracker_free+0x610/0x830 lib/ref_tracker.c:255
Code: 00 00 44 8b 73 18 31 ff 44 89 f6 e8 7a 58 fe fc 45 85 f6 0f 85
a7 00 00 00 e8 4c 5c fe fc 4c 89 ee 48 89 ef e8 11 0a e5 05 90 <0f> 0b
90 41 bd ea ff ff ff e9 51 fd ff ff e8 2d 5c fe fc 4c 8d 75
RSP: 0018:ffffc900029bf8b8 EFLAGS: 00010286
RAX: 0000000080000000 RBX: ffff888106185480 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000001 RDI: 0000000000000001
RBP: ffff8881136c85b8 R08: 0000000000000001 R09: fffffbfff23e8bd1
R10: 0000000000000001 R11: 0000000000000001 R12: 1ffff92000537f19
R13: 0000000000000292 R14: 00000000067a01d1 R15: ffff888106185498
FS:  0000555556e663c0(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc148041ba8 CR3: 0000000016374000 CR4: 0000000000750ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 <TASK>
 netdev_tracker_free include/linux/netdevice.h:4127 [inline]
 netdev_put include/linux/netdevice.h:4144 [inline]
 netdev_put include/linux/netdevice.h:4140 [inline]
 ax25_dev_device_down+0x2bc/0x420 net/ax25/ax25_dev.c:140
 ax25_device_event+0x4bc/0x650 net/ax25/af_ax25.c:148
 notifier_call_chain+0xb6/0x3d0 kernel/notifier.c:93
 call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:1967
 call_netdevice_notifiers_extack net/core/dev.c:2005 [inline]
 call_netdevice_notifiers net/core/dev.c:2019 [inline]
 __dev_notify_flags+0x1f5/0x2e0 net/core/dev.c:8649
 dev_change_flags+0x11b/0x170 net/core/dev.c:8685
 change_flags net/core/net-sysfs.c:371 [inline]
 netdev_store net/core/net-sysfs.c:100 [inline]
 flags_store+0x1ba/0x240 net/core/net-sysfs.c:377
 dev_attr_store+0x54/0x80 drivers/base/core.c:2366
 sysfs_kf_write+0x114/0x170 fs/sysfs/file.c:136
 kernfs_fop_write_iter+0x337/0x500 fs/kernfs/file.c:334
 call_write_iter include/linux/fs.h:2020 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x96a/0xd80 fs/read_write.c:584
 ksys_write+0x122/0x250 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f80fd95f697
Code: ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f
1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d
00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
RSP: 002b:00007ffed044c0b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007f80fd95f697
RDX: 0000000000000004 RSI: 00007ffed044c8d0 RDI: 0000000000000007
RBP: 0000000000000007 R08: 000000000000000f R09: 0074656e2d74736f
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffed044c8d0
R13: 00007ffed044c4d0 R14: 00007f80fd9dd4f0 R15: 0000000000000001
 </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

// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.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;
}

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;
}

const int kInitNetNsFd = 201;

static long syz_mod_dev(volatile long a0, volatile long a1, volatile long a2,
                        volatile long a3, volatile long a4, volatile long a5)
{
  int fd, sysfd;
  char buf[1024], sysbuf[1024], input[1024];
  char* hash;
  char dev_num;
  dev_num = '\0';
  strncpy(buf, (char*)a0, sizeof(buf) - 1);
  buf[sizeof(buf) - 1] = 0;
  while ((hash = strchr(buf, '#'))) {
    *hash = '0' + (char)(a1 % 10);
    a1 /= 10;
    if (dev_num == '\0')
      dev_num = *hash;
  }
  fd = open(buf, a2, 0);
  strncpy(sysbuf, (char*)a3, sizeof(sysbuf) - 1);
  sysbuf[sizeof(sysbuf) - 1] = 0;
  if ((hash = strchr(sysbuf, '#'))) {
    *hash = dev_num;
    while ((hash = strchr(sysbuf, '#'))) {
      *hash = '0' + (char)(a1 % 10);
      a1 /= 10;
    }
  }
  sysfd = open(sysbuf, O_RDWR, 0);
  strncpy(input, (char*)a4, sizeof(input) - 1);
  input[sizeof(input) - 1] = 0;
  hash = strchr(input, '\0');
  sysfd = write(sysfd, input, hash - input + 1);
  return fd;
}

static long syz_init_net_socket(volatile long domain, volatile long type,
                                volatile long proto)
{
  return syscall(__NR_socket, domain, type, proto);
}

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");
}

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;
    }
  }
}

uint64_t r[1] = {0xffffffffffffffff};

void execute_one(void)
{
  intptr_t res = 0;
  memcpy((void*)0x20000040, "/dev/vhost-net\000", 15);
  memcpy((void*)0x20000080, "/sys/devices/virtual/net/bpq0/flags\000", 36);
  memcpy((void*)0x200000c0, "1\000", 2);
  syz_mod_dev(/*dev=*/0x20000040, /*id=*/6, /*flags=*/0x100000,
              /*file=*/0x20000080, /*buf=*/0x200000c0, /*fd=*/-1);
  res = -1;
  res =
      syz_init_net_socket(/*domain=*/3, /*type=SOCK_SEQPACKET*/ 5, /*proto=*/0);
  if (res != -1)
    r[0] = res;
  *(uint16_t*)0x20000100 = 3;
  *(uint8_t*)0x20000102 = 0x98;
  *(uint8_t*)0x20000103 = 0x92;
  *(uint8_t*)0x20000104 = 0x9c;
  *(uint8_t*)0x20000105 = 0xaa;
  *(uint8_t*)0x20000106 = 0xb0;
  *(uint8_t*)0x20000107 = 0x40;
  *(uint8_t*)0x20000108 = 2;
  *(uint32_t*)0x2000010c = 0;
  *(uint8_t*)0x20000110 = 0x40;
  *(uint8_t*)0x20000111 = 0x40;
  *(uint8_t*)0x20000112 = 0x40;
  *(uint8_t*)0x20000113 = 0x40;
  *(uint8_t*)0x20000114 = 0x40;
  *(uint8_t*)0x20000115 = 0x40;
  *(uint8_t*)0x20000116 = 0;
  *(uint8_t*)0x20000117 = 0x40;
  *(uint8_t*)0x20000118 = 0x40;
  *(uint8_t*)0x20000119 = 0x40;
  *(uint8_t*)0x2000011a = 0x40;
  *(uint8_t*)0x2000011b = 0x40;
  *(uint8_t*)0x2000011c = 0x40;
  *(uint8_t*)0x2000011d = 0;
  *(uint8_t*)0x2000011e = 0x98;
  *(uint8_t*)0x2000011f = 0x92;
  *(uint8_t*)0x20000120 = 0x9c;
  *(uint8_t*)0x20000121 = 0xaa;
  *(uint8_t*)0x20000122 = 0xb0;
  *(uint8_t*)0x20000123 = 0x40;
  *(uint8_t*)0x20000124 = 2;
  *(uint8_t*)0x20000125 = 0xcc;
  *(uint8_t*)0x20000126 = 0xcc;
  *(uint8_t*)0x20000127 = 0xcc;
  *(uint8_t*)0x20000128 = 0xcc;
  *(uint8_t*)0x20000129 = 0xcc;
  *(uint8_t*)0x2000012a = 0xcc;
  *(uint8_t*)0x2000012b = 2;
  *(uint8_t*)0x2000012c = 0x98;
  *(uint8_t*)0x2000012d = 0x92;
  *(uint8_t*)0x2000012e = 0x9c;
  *(uint8_t*)0x2000012f = 0xaa;
  *(uint8_t*)0x20000130 = 0xb0;
  *(uint8_t*)0x20000131 = 0x40;
  *(uint8_t*)0x20000132 = 2;
  *(uint8_t*)0x20000133 = 0x40;
  *(uint8_t*)0x20000134 = 0x40;
  *(uint8_t*)0x20000135 = 0x40;
  *(uint8_t*)0x20000136 = 0x40;
  *(uint8_t*)0x20000137 = 0x40;
  *(uint8_t*)0x20000138 = 0x40;
  *(uint8_t*)0x20000139 = 0;
  *(uint8_t*)0x2000013a = 0x98;
  *(uint8_t*)0x2000013b = 0x92;
  *(uint8_t*)0x2000013c = 0x9c;
  *(uint8_t*)0x2000013d = 0xaa;
  *(uint8_t*)0x2000013e = 0xb0;
  *(uint8_t*)0x2000013f = 0x40;
  *(uint8_t*)0x20000140 = 2;
  *(uint8_t*)0x20000141 = 0x98;
  *(uint8_t*)0x20000142 = 0x92;
  *(uint8_t*)0x20000143 = 0x9c;
  *(uint8_t*)0x20000144 = 0xaa;
  *(uint8_t*)0x20000145 = 0xb0;
  *(uint8_t*)0x20000146 = 0x40;
  *(uint8_t*)0x20000147 = 2;
  syscall(__NR_bind, /*fd=*/r[0], /*addr=*/0x20000100ul, /*addrlen=*/0x48ul);
  memcpy((void*)0x20000040, "/dev/vhost-net\000", 15);
  memcpy((void*)0x20000080, "/sys/devices/virtual/net/bpq0/flags\000", 36);
  memcpy((void*)0x20000000, "100\000", 4);
  syz_mod_dev(/*dev=*/0x20000040, /*id=*/6, /*flags=*/0x100000,
              /*file=*/0x20000080, /*buf=*/0x20000000, /*fd=*/-1);
}
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;
}