net/ipv4: warning in nf_nat_ipv4_fn

[Andrey Konovalov]

Hi,

I've got the following error report while fuzzing the kernel with syzkaller.

On commit 926af6273fc683cd98cd0ce7bf0d04a02eed6742.

A reproducer and .config are attached.

WARNING: CPU: 2 PID: 26582 at
net/ipv4/netfilter/nf_nat_l3proto_ipv4.c:261
nf_nat_ipv4_fn+0x7f2/0xa50
net/ipv4/netfilter/nf_nat_l3proto_ipv4.c:261
Kernel panic - not syncing: panic_on_warn set ...

CPU: 2 PID: 26582 Comm: syz-executor2 Not tainted 4.10.0-rc7+ #126
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:15 [inline]
 dump_stack+0x292/0x398 lib/dump_stack.c:51
 panic+0x1cb/0x3a9 kernel/panic.c:179
 __warn+0x1c4/0x1e0 kernel/panic.c:539
 warn_slowpath_null+0x2c/0x40 kernel/panic.c:582
 nf_nat_ipv4_fn+0x7f2/0xa50 net/ipv4/netfilter/nf_nat_l3proto_ipv4.c:261
 nf_nat_ipv4_local_fn+0x1be/0x6d0 net/ipv4/netfilter/nf_nat_l3proto_ipv4.c:414
 iptable_nat_ipv4_local_fn+0x2c/0x40 net/ipv4/netfilter/iptable_nat.c:67
 nf_hook_entry_hookfn include/linux/netfilter.h:102 [inline]
 nf_hook_slow+0xc3/0x290 net/netfilter/core.c:310
 nf_hook include/linux/netfilter.h:212 [inline]
 NF_HOOK include/linux/netfilter.h:255 [inline]
 raw_send_hdrinc net/ipv4/raw.c:420 [inline]
 raw_sendmsg+0x2bab/0x38e0 net/ipv4/raw.c:637
 inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:744
 sock_sendmsg_nosec net/socket.c:635 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:645
 sock_write_iter+0x326/0x620 net/socket.c:848
 new_sync_write fs/read_write.c:499 [inline]
 __vfs_write+0x483/0x760 fs/read_write.c:512
 vfs_write+0x187/0x530 fs/read_write.c:560
 SYSC_write fs/read_write.c:607 [inline]
 SyS_write+0xfb/0x230 fs/read_write.c:599
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x4458b9
RSP: 002b:00007f0e76be1b58 EFLAGS: 00000292 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00000000004458b9
RDX: 000000000000004f RSI: 0000000020009000 RDI: 0000000000000005
RBP: 00000000006e2fd0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000292 R12: 00000000007080a8
R13: 0000000000000000 R14: 00007f0e76be29c0 R15: 00007f0e76be2700
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..
// autogenerated by syzkaller (http://github.com/google/syzkaller)

#ifndef __NR_connect
#define __NR_connect 42
#endif
#ifndef __NR_setsockopt
#define __NR_setsockopt 54
#endif
#ifndef __NR_write
#define __NR_write 1
#endif
#ifndef __NR_mmap
#define __NR_mmap 9
#endif
#ifndef __NR_socket
#define __NR_socket 41
#endif

#define _GNU_SOURCE

#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/resource.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>

#include <linux/capability.h>
#include <linux/if.h>
#include <linux/if_tun.h>
#include <linux/kvm.h>
#include <linux/sched.h>
#include <net/if_arp.h>

#include <assert.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <pthread.h>
#include <setjmp.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

const int kFailStatus = 67;
const int kErrorStatus = 68;
const int kRetryStatus = 69;

__attribute__((noreturn)) void doexit(int status)
{
  volatile unsigned i;
  syscall(__NR_exit_group, status);
  for (i = 0;; i++) {
  }
}

__attribute__((noreturn)) void fail(const char* msg, ...)
{
  int e = errno;
  fflush(stdout);
  va_list args;
  va_start(args, msg);
  vfprintf(stderr, msg, args);
  va_end(args);
  fprintf(stderr, " (errno %d)\n", e);
  doexit(e == ENOMEM ? kRetryStatus : kFailStatus);
}

__attribute__((noreturn)) void exitf(const char* msg, ...)
{
  int e = errno;
  fflush(stdout);
  va_list args;
  va_start(args, msg);
  vfprintf(stderr, msg, args);
  va_end(args);
  fprintf(stderr, " (errno %d)\n", e);
  doexit(kRetryStatus);
}

static int flag_debug;

void debug(const char* msg, ...)
{
  if (!flag_debug)
    return;
  va_list args;
  va_start(args, msg);
  vfprintf(stdout, msg, args);
  va_end(args);
  fflush(stdout);
}

__thread int skip_segv;
__thread jmp_buf segv_env;

static void segv_handler(int sig, siginfo_t* info, void* uctx)
{
  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)) {
    debug("SIGSEGV on %p, skipping\n", addr);
    _longjmp(segv_env, 1);
  }
  debug("SIGSEGV on %p, exiting\n", addr);
  doexit(sig);
  for (;;) {
  }
}

static void install_segv_handler()
{
  struct sigaction sa;
  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);               \
  }

#define BITMASK_LEN(type, bf_len) (type)((1ull << (bf_len)) - 1)

#define BITMASK_LEN_OFF(type, bf_off, bf_len)                          \
  (type)(BITMASK_LEN(type, (bf_len)) << (bf_off))

#define STORE_BY_BITMASK(type, addr, val, bf_off, bf_len)              \
  if ((bf_off) == 0 && (bf_len) == 0) {                                \
    *(type*)(addr) = (type)(val);                                      \
  } else {                                                             \
    type new_val = *(type*)(addr);                                     \
    new_val &= ~BITMASK_LEN_OFF(type, (bf_off), (bf_len));             \
    new_val |= ((type)(val)&BITMASK_LEN(type, (bf_len))) << (bf_off);  \
    *(type*)(addr) = new_val;                                          \
  }

static uintptr_t execute_syscall(int nr, uintptr_t a0, uintptr_t a1,
                                 uintptr_t a2, uintptr_t a3,
                                 uintptr_t a4, uintptr_t a5,
                                 uintptr_t a6, uintptr_t a7,
                                 uintptr_t a8)
{
  switch (nr) {
  default:
    return syscall(nr, a0, a1, a2, a3, a4, a5);
  }
}

static void setup_main_process()
{
  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);
  install_segv_handler();

  char tmpdir_template[] = "./syzkaller.XXXXXX";
  char* tmpdir = mkdtemp(tmpdir_template);
  if (!tmpdir)
    fail("failed to mkdtemp");
  if (chmod(tmpdir, 0777))
    fail("failed to chmod");
  if (chdir(tmpdir))
    fail("failed to chdir");
}

static void loop();

static void sandbox_common()
{
  prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
  setpgrp();
  setsid();

  struct rlimit rlim;
  rlim.rlim_cur = rlim.rlim_max = 128 << 20;
  setrlimit(RLIMIT_AS, &rlim);
  rlim.rlim_cur = rlim.rlim_max = 1 << 20;
  setrlimit(RLIMIT_FSIZE, &rlim);
  rlim.rlim_cur = rlim.rlim_max = 1 << 20;
  setrlimit(RLIMIT_STACK, &rlim);
  rlim.rlim_cur = rlim.rlim_max = 0;
  setrlimit(RLIMIT_CORE, &rlim);

  unshare(CLONE_NEWNS);
  unshare(CLONE_NEWIPC);
  unshare(CLONE_IO);
}

static int do_sandbox_none(int executor_pid, bool enable_tun)
{
  int pid = fork();
  if (pid)
    return pid;

  sandbox_common();

  loop();
  doexit(1);
}

long r[20];
void loop()
{
  memset(r, -1, sizeof(r));
  r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0xa000ul, 0x3ul,
                         0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
  r[1] = execute_syscall(__NR_socket, 0x2ul, 0x3ul, 0x1ul, 0, 0, 0, 0,
                         0, 0);
  NONFAILING(*(uint16_t*)0x20003000 = (uint16_t)0x2);
  NONFAILING(*(uint16_t*)0x20003002 = (uint16_t)0x204e);
  NONFAILING(*(uint32_t*)0x20003004 = (uint32_t)0x100007f);
  NONFAILING(*(uint8_t*)0x20003008 = (uint8_t)0x0);
  NONFAILING(*(uint8_t*)0x20003009 = (uint8_t)0x0);
  NONFAILING(*(uint8_t*)0x2000300a = (uint8_t)0x0);
  NONFAILING(*(uint8_t*)0x2000300b = (uint8_t)0x0);
  NONFAILING(*(uint8_t*)0x2000300c = (uint8_t)0x0);
  NONFAILING(*(uint8_t*)0x2000300d = (uint8_t)0x0);
  NONFAILING(*(uint8_t*)0x2000300e = (uint8_t)0x0);
  NONFAILING(*(uint8_t*)0x2000300f = (uint8_t)0x0);
  r[13] = execute_syscall(__NR_connect, r[1], 0x20003000ul, 0x10ul, 0,
                          0, 0, 0, 0, 0);
  NONFAILING(*(uint32_t*)0x20002ffc = (uint32_t)0xf28);
  r[15] = execute_syscall(__NR_setsockopt, r[1], 0x0ul, 0x3ul,
                          0x20002ffcul, 0x4ul, 0, 0, 0, 0);
  NONFAILING(*(uint32_t*)0x20007000 = (uint32_t)0x7fffffff);
  r[17] = execute_syscall(__NR_setsockopt, r[1], 0x0ul, 0x16ul,
                          0x20007000ul, 0x4ul, 0, 0, 0, 0);
  NONFAILING(memcpy(
      (void*)0x20009000,
      "\x7e\x50\x9c\x60\x97\x35\x23\x9e\xff\xe5\x55\xac\x59\xde\x74\x9e"
      "\x9b\xae\xbd\x30\xdb\xc5\x81\x8f\x02\x7b\xb4\xee\x1e\xc8\x4e\xee"
      "\xe6\x1b\x9b\x12\x77\x5f\x19\xf5\xb4\xf6\x0d\x46\x70\x86\xaf\x08"
      "\x88\x89\x9f\x52\x17\x64\x60\x98\x2b\x4d\x52\x5a\x44\x17\x92\xcd"
      "\xb1\x09\xa5\xf6\xb9\x4a\x06\x03\xf8\x73\xf4\x64\x31\x14\x8b",
      79));
  r[19] = execute_syscall(__NR_write, r[1], 0x20009000ul, 0x4ful, 0, 0,
                          0, 0, 0, 0);
}
int main()
{
  setup_main_process();
  int pid = do_sandbox_none(0, false);
  int status = 0;
  while (waitpid(pid, &status, __WALL) != pid) {
  }
  return 0;
}

Attachment: .config
Description: Binary data