On Thu, Oct 17, 2019 at 10:47:59AM -0500, Mike Christie wrote:

On 10/17/2019 09:03 AM, Richard W.M. Jones wrote:

quoted

On Tue, Oct 01, 2019 at 04:19:25PM -0500, Mike Christie wrote:

quoted

Hey Josef and nbd list,

I had a question about if there are any socket family restrictions for nbd?

In normal circumstances, in userspace, the NBD protocol would only be
used over AF_UNIX or AF_INET/AF_INET6.

There's a bit of confusion because netlink is used by nbd-client to
configure the NBD device, setting things like block size and timeouts
(instead of ioctl which is deprecated).  I think you don't mean this
use of netlink?

I didn't. It looks like it is just a bad test.

For the automated test in this thread the test created a AF_NETLINK
socket and passed it into the NBD_SET_SOCK ioctl. That is what got used
for the NBD_DO_IT ioctl.

I was not sure if the test creator picked any old socket and it just
happened to pick one nbd never supported, or it was trying to simulate
sockets that did not support the shutdown method.

I attached the automated test that got run (test.c).

I'd say it sounds like a bad test, but I'm not familiar with syzkaller
nor how / from where it generates these tests.  Did someone report a
bug and then syzkaller wrote this test?

Rich.

quoted

quoted

The bug here is that some socket familys do not support the
sock->ops->shutdown callout, and when nbd calls kernel_sock_shutdown
their callout returns -EOPNOTSUPP. That then leaves recv_work stuck in
nbd_read_stat -> sock_xmit -> sock_recvmsg. My patch added a
flush_workqueue call, so for socket familys like AF_NETLINK in this bug
we hang like we see below.

I can just remove the flush_workqueue call in that code path since it's
not needed there, but it leaves the original bug my patch was hitting
where we leave the recv_work running which can then result in leaked
resources, or possible use after free crashes and you still get the hang
if you remove the module.

It looks like we have used kernel_sock_shutdown for a while so I thought
we might never have supported sockets that did not support the callout.
Is that correct? If so then I can just add a check for this in
nbd_add_socket and fix that bug too.

Rich.

quoted

On 09/30/2019 05:39 PM, syzbot wrote:

quoted

Hello,

syzbot found the following crash on:

HEAD commit:    bb2aee77 Add linux-next specific files for 20190926
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13385ca3600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e60af4ac5a01e964
dashboard link:
https://syzkaller.appspot.com/bug?extid=24c12fa8d218ed26011a
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12abc2a3600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11712c05600000

The bug was bisected to:

commit e9e006f5fcf2bab59149cb38a48a4817c1b538b4
Author: Mike Christie [off-list ref]
Date:   Sun Aug 4 19:10:06 2019 +0000

    nbd: fix max number of supported devs

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1226f3c5600000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1126f3c5600000
console output: https://syzkaller.appspot.com/x/log.txt?x=1626f3c5600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+24c12fa8d218ed26011a@syzkaller.appspotmail.com
Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs")

INFO: task syz-executor390:8778 can't die for more than 143 seconds.
syz-executor390 D27432  8778   8777 0x00004004
Call Trace:
 context_switch kernel/sched/core.c:3384 [inline]
 __schedule+0x828/0x1c20 kernel/sched/core.c:4065
 schedule+0xd9/0x260 kernel/sched/core.c:4132
 schedule_timeout+0x717/0xc50 kernel/time/timer.c:1871
 do_wait_for_common kernel/sched/completion.c:83 [inline]
 __wait_for_common kernel/sched/completion.c:104 [inline]
 wait_for_common kernel/sched/completion.c:115 [inline]
 wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
 flush_workqueue+0x40f/0x14c0 kernel/workqueue.c:2826
 nbd_start_device_ioctl drivers/block/nbd.c:1272 [inline]
 __nbd_ioctl drivers/block/nbd.c:1347 [inline]
 nbd_ioctl+0xb2e/0xc44 drivers/block/nbd.c:1387
 __blkdev_driver_ioctl block/ioctl.c:304 [inline]
 blkdev_ioctl+0xedb/0x1c20 block/ioctl.c:606
 block_ioctl+0xee/0x130 fs/block_dev.c:1954
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:539 [inline]
 do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
 __do_sys_ioctl fs/ioctl.c:750 [inline]
 __se_sys_ioctl fs/ioctl.c:748 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4452d9
Code: Bad RIP value.
RSP: 002b:00007ffde928d288 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004452d9
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
RBP: 0000000000000000 R08: 00000000004025b0 R09: 00000000004025b0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402520
R13: 00000000004025b0 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor390:8778 blocked for more than 143 seconds.
      Not tainted 5.3.0-next-20190926 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor390 D27432  8778   8777 0x00004004
Call Trace:
 context_switch kernel/sched/core.c:3384 [inline]
 __schedule+0x828/0x1c20 kernel/sched/core.c:4065
 schedule+0xd9/0x260 kernel/sched/core.c:4132
 schedule_timeout+0x717/0xc50 kernel/time/timer.c:1871
 do_wait_for_common kernel/sched/completion.c:83 [inline]
 __wait_for_common kernel/sched/completion.c:104 [inline]
 wait_for_common kernel/sched/completion.c:115 [inline]
 wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
 flush_workqueue+0x40f/0x14c0 kernel/workqueue.c:2826
 nbd_start_device_ioctl drivers/block/nbd.c:1272 [inline]
 __nbd_ioctl drivers/block/nbd.c:1347 [inline]
 nbd_ioctl+0xb2e/0xc44 drivers/block/nbd.c:1387
 __blkdev_driver_ioctl block/ioctl.c:304 [inline]
 blkdev_ioctl+0xedb/0x1c20 block/ioctl.c:606
 block_ioctl+0xee/0x130 fs/block_dev.c:1954
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:539 [inline]
 do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
 __do_sys_ioctl fs/ioctl.c:750 [inline]
 __se_sys_ioctl fs/ioctl.c:748 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4452d9
Code: Bad RIP value.
RSP: 002b:00007ffde928d288 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004452d9
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
RBP: 0000000000000000 R08: 00000000004025b0 R09: 00000000004025b0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402520
R13: 00000000004025b0 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1066:
 #0: ffffffff88faad80 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:5337
2 locks held by kworker/u5:0/1525:
 #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
__write_once_size include/linux/compiler.h:226 [inline]
 #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:855 [inline]
 #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
atomic_long_set include/asm-generic/atomic-long.h:40 [inline]
 #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
set_work_data kernel/workqueue.c:620 [inline]
 #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline]
 #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
process_one_work+0x88b/0x1740 kernel/workqueue.c:2240
 #1: ffff8880a63b7dc0 ((work_completion)(&args->work)){+.+.}, at:
process_one_work+0x8c1/0x1740 kernel/workqueue.c:2244
1 lock held by rsyslogd/8659:
2 locks held by getty/8749:
 #0: ffff888098c08090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
 #1: ffffc90005f112e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/8750:
 #0: ffff88808f10b090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
 #1: ffffc90005f2d2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/8751:
 #0: ffff88809a6be090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
 #1: ffffc90005f192e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/8752:
 #0: ffff8880a48af090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
 #1: ffffc90005f352e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/8753:
 #0: ffff88808c599090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
 #1: ffffc90005f212e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/8754:
 #0: ffff88808f1a8090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
 #1: ffffc90005f392e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
2 locks held by getty/8755:
 #0: ffff88809ab33090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
 #1: ffffc90005f012e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1066 Comm: khungtaskd Not tainted 5.3.0-next-20190926 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x23b/0x28b lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:269 [inline]
 watchdog+0xc99/0x1360 kernel/hung_task.c:353
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10
arch/x86/include/asm/irqflags.h:60


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see:
https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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

#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <setjmp.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 __thread int skip_segv;
static __thread jmp_buf segv_env;

static void segv_handler(int sig, siginfo_t* info, void* ctx)
{
  uintptr_t addr = (uintptr_t)info->si_addr;
  const uintptr_t prog_start = 1 << 20;
  const uintptr_t prog_end = 100 << 20;
  if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED) &&
      (addr < prog_start || addr > prog_end)) {
    _longjmp(segv_env, 1);
  }
  exit(sig);
}

static void install_segv_handler(void)
{
  struct sigaction sa;
  memset(&sa, 0, sizeof(sa));
  sa.sa_handler = SIG_IGN;
  syscall(SYS_rt_sigaction, 0x20, &sa, NULL, 8);
  syscall(SYS_rt_sigaction, 0x21, &sa, NULL, 8);
  memset(&sa, 0, sizeof(sa));
  sa.sa_sigaction = segv_handler;
  sa.sa_flags = SA_NODEFER | SA_SIGINFO;
  sigaction(SIGSEGV, &sa, NULL);
  sigaction(SIGBUS, &sa, NULL);
}

#define NONFAILING(...)                                                        \
  {                                                                            \
    __atomic_fetch_add(&skip_segv, 1, __ATOMIC_SEQ_CST);                       \
    if (_setjmp(segv_env) == 0) {                                              \
      __VA_ARGS__;                                                             \
    }                                                                          \
    __atomic_fetch_sub(&skip_segv, 1, __ATOMIC_SEQ_CST);                       \
  }

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;
}

static long syz_open_dev(volatile long a0, volatile long a1, volatile long a2)
{
  if (a0 == 0xc || a0 == 0xb) {
    char buf[128];
    sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block", (uint8_t)a1,
            (uint8_t)a2);
    return open(buf, O_RDWR, 0);
  } else {
    char buf[1024];
    char* hash;
    NONFAILING(strncpy(buf, (char*)a0, sizeof(buf) - 1));
    buf[sizeof(buf) - 1] = 0;
    while ((hash = strchr(buf, '#'))) {
      *hash = '0' + (char)(a1 % 10);
      a1 /= 10;
    }
    return open(buf, a2, 0);
  }
}

static void kill_and_wait(int pid, int* status)
{
  kill(-pid, SIGKILL);
  kill(pid, SIGKILL);
  int i;
  for (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;
  for (iter = 0; iter < 1; 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 < 5 * 1000)
        continue;
      kill_and_wait(pid, &status);
      break;
    }
  }
}

uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};

void execute_one(void)
{
  intptr_t res = 0;
  res = syscall(__NR_socket, 0x10, 2, 2);
  if (res != -1)
    r[0] = res;
  NONFAILING(memcpy((void*)0x20000080, "/dev/nbd#\000", 10));
  res = syz_open_dev(0x20000080, 0, 0);
  if (res != -1)
    r[1] = res;
  res = syz_open_dev(0, 0, 0);
  if (res != -1)
    r[2] = res;
  syscall(__NR_ioctl, r[2], 0xab00, r[0]);
  syscall(__NR_ioctl, r[1], 0xab03, 0);
}
int main(void)
{
  syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
  install_segv_handler();
  loop();
  return 0;
}

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
Fedora Windows cross-compiler. Compile Windows programs, test, and
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