net/ipv6: use-after-free in sock_wfree

[Andrey Konovalov <andreyknvl@google.com>]

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Hi!

I've got the following error report while running the syzkaller fuzzer.

On commit a121103c922847ba5010819a3f250f1f7fc84ab8 (4.10-rc3).

A reproducer is attached.

==================================================================
BUG: KASAN: use-after-free in sock_wfree+0x118/0x120
Read of size 8 at addr ffff880062da0060 by task a.out/4140

page:ffffea00018b6800 count:1 mapcount:0 mapping:          (null)
index:0x0 compound_mapcount: 0
flags: 0x100000000008100(slab|head)
raw: 0100000000008100 0000000000000000 0000000000000000 0000000180130013
raw: dead000000000100 dead000000000200 ffff88006741f140 0000000000000000
page dumped because: kasan: bad access detected

CPU: 0 PID: 4140 Comm: a.out Not tainted 4.10.0-rc3+ #59
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:15
 dump_stack+0x292/0x398 lib/dump_stack.c:51
 describe_address mm/kasan/report.c:262
 kasan_report_error+0x121/0x560 mm/kasan/report.c:370
 kasan_report mm/kasan/report.c:392
 __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:413
 sock_flag ./arch/x86/include/asm/bitops.h:324
 sock_wfree+0x118/0x120 net/core/sock.c:1631
 skb_release_head_state+0xfc/0x250 net/core/skbuff.c:655
 skb_release_all+0x15/0x60 net/core/skbuff.c:668
 __kfree_skb+0x15/0x20 net/core/skbuff.c:684
 kfree_skb+0x16e/0x4e0 net/core/skbuff.c:705
 inet_frag_destroy+0x121/0x290 net/ipv4/inet_fragment.c:304
 inet_frag_put ./include/net/inet_frag.h:133
 nf_ct_frag6_gather+0x1125/0x38b0 net/ipv6/netfilter/nf_conntrack_reasm.c:617
 ipv6_defrag+0x21b/0x350 net/ipv6/netfilter/nf_defrag_ipv6_hooks.c:68
 nf_hook_entry_hookfn ./include/linux/netfilter.h:102
 nf_hook_slow+0xc3/0x290 net/netfilter/core.c:310
 nf_hook ./include/linux/netfilter.h:212
 __ip6_local_out+0x52c/0xaf0 net/ipv6/output_core.c:160
 ip6_local_out+0x2d/0x170 net/ipv6/output_core.c:170
 ip6_send_skb+0xa1/0x340 net/ipv6/ip6_output.c:1722
 ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1742
 rawv6_push_pending_frames net/ipv6/raw.c:613
 rawv6_sendmsg+0x2cff/0x4130 net/ipv6/raw.c:927
 inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:744
 sock_sendmsg_nosec net/socket.c:635
 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
 __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
 SyS_write+0xfb/0x230 fs/read_write.c:599
 entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:203
RIP: 0033:0x7ff26e6f5b79
RSP: 002b:00007ff268e0ed98 EFLAGS: 00000206 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007ff268e0f9c0 RCX: 00007ff26e6f5b79
RDX: 0000000000000010 RSI: 0000000020f50fe1 RDI: 0000000000000003
RBP: 00007ff26ebc1220 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007ff268e0f9c0 R14: 00007ff26efec040 R15: 0000000000000003

The buggy address belongs to the object at ffff880062da0000
 which belongs to the cache RAWv6 of size 1504
The buggy address ffff880062da0060 is located 96 bytes inside
 of 1504-byte region [ffff880062da0000, ffff880062da05e0)

Freed by task 4113:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:502
 set_track mm/kasan/kasan.c:514
 kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:578
 slab_free_hook mm/slub.c:1352
 slab_free_freelist_hook mm/slub.c:1374
 slab_free mm/slub.c:2951
 kmem_cache_free+0xb2/0x2c0 mm/slub.c:2973
 sk_prot_free net/core/sock.c:1377
 __sk_destruct+0x49c/0x6e0 net/core/sock.c:1452
 sk_destruct+0x47/0x80 net/core/sock.c:1460
 __sk_free+0x57/0x230 net/core/sock.c:1468
 sk_free+0x23/0x30 net/core/sock.c:1479
 sock_put ./include/net/sock.h:1638
 sk_common_release+0x31e/0x4e0 net/core/sock.c:2782
 rawv6_close+0x54/0x80 net/ipv6/raw.c:1214
 inet_release+0xed/0x1c0 net/ipv4/af_inet.c:425
 inet6_release+0x50/0x70 net/ipv6/af_inet6.c:431
 sock_release+0x8d/0x1e0 net/socket.c:599
 sock_close+0x16/0x20 net/socket.c:1063
 __fput+0x332/0x7f0 fs/file_table.c:208
 ____fput+0x15/0x20 fs/file_table.c:244
 task_work_run+0x19b/0x270 kernel/task_work.c:116
 exit_task_work ./include/linux/task_work.h:21
 do_exit+0x186b/0x2800 kernel/exit.c:839
 do_group_exit+0x149/0x420 kernel/exit.c:943
 SYSC_exit_group kernel/exit.c:954
 SyS_exit_group+0x1d/0x20 kernel/exit.c:952
 entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:203

Allocated by task 4115:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:502
 set_track mm/kasan/kasan.c:514
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:605
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:544
 slab_post_alloc_hook mm/slab.h:432
 slab_alloc_node mm/slub.c:2708
 slab_alloc mm/slub.c:2716
 kmem_cache_alloc+0x1af/0x250 mm/slub.c:2721
 sk_prot_alloc+0x65/0x2a0 net/core/sock.c:1334
 sk_alloc+0x105/0x1010 net/core/sock.c:1396
 inet6_create+0x44d/0x1150 net/ipv6/af_inet6.c:183
 __sock_create+0x4f6/0x880 net/socket.c:1199
 sock_create net/socket.c:1239
 SYSC_socket net/socket.c:1269
 SyS_socket+0xf9/0x230 net/socket.c:1249
 entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:203

Memory state around the buggy address:
 ffff880062d9ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff880062d9ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff880062da0000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff880062da0080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff880062da0100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

[-- Attachment #2: ipv6-wfree-uaf-poc.c --]
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// autogenerated by syzkaller (http://github.com/google/syzkaller)

#ifndef __NR_ioctl
#define __NR_ioctl 16
#endif
#ifndef __NR_mmap
#define __NR_mmap 9
#endif
#ifndef __NR_socket
#define __NR_socket 41
#endif
#ifndef __NR_connect
#define __NR_connect 42
#endif
#ifndef __NR_bind
#define __NR_bind 49
#endif
#ifndef __NR_sendto
#define __NR_sendto 44
#endif
#ifndef __NR_recvfrom
#define __NR_recvfrom 45
#endif
#ifndef __NR_write
#define __NR_write 1
#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/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)
{
  syscall(__NR_exit_group, status);
  volatile unsigned i = 0;
  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)
{
  if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED))
    _longjmp(segv_env, 1);
  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);               \
  }

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(uint64_t pid, bool enable_tun)
{
  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 pid = fork();
  if (pid)
    return pid;
  sandbox_common();
  loop();
  doexit(1);
}

long r[56];
void* thr(void* arg)
{
  switch ((long)arg) {
  case 0:
    r[0] =
        execute_syscall(__NR_mmap, 0x20000000ul, 0xf55000ul, 0x3ul,
                        0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
    break;
  case 1:
    r[1] = execute_syscall(__NR_socket, 0xaul, 0x3ul, 0x2cul, 0, 0, 0,
                           0, 0, 0);
    break;
  case 2:
    NONFAILING(*(uint16_t*)0x20016000 = (uint16_t)0xa);
    NONFAILING(*(uint16_t*)0x20016002 = (uint16_t)0x204e);
    NONFAILING(*(uint32_t*)0x20016004 = (uint32_t)0x0);
    NONFAILING(*(uint64_t*)0x20016008 = (uint64_t)0x0);
    NONFAILING(*(uint64_t*)0x20016010 = (uint64_t)0x0);
    NONFAILING(*(uint32_t*)0x20016018 = (uint32_t)0x0);
    r[8] = execute_syscall(__NR_connect, r[1], 0x20016000ul, 0x20ul, 0,
                           0, 0, 0, 0, 0);
    break;
  case 3:
    NONFAILING(*(uint16_t*)0x20373000 = (uint16_t)0x2);
    NONFAILING(*(uint16_t*)0x20373002 = (uint16_t)0x204e);
    NONFAILING(*(uint8_t*)0x20373004 = (uint8_t)0xc0);
    NONFAILING(*(uint8_t*)0x20373005 = (uint8_t)0xa8);
    NONFAILING(*(uint8_t*)0x20373006 = (uint8_t)0xda);
    NONFAILING(*(uint8_t*)0x20373007 = (uint8_t)0xaa);
    NONFAILING(*(uint8_t*)0x20373008 = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20373009 = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x2037300a = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x2037300b = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x2037300c = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x2037300d = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x2037300e = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x2037300f = (uint8_t)0x0);
    r[23] = execute_syscall(__NR_bind, 0xfffffffffffffffful,
                            0x20373000ul, 0x10ul, 0, 0, 0, 0, 0, 0);
    break;
  case 4:
    NONFAILING(*(uint16_t*)0x20f4a000 = (uint16_t)0x0);
    NONFAILING(*(uint16_t*)0x20f4a002 = (uint16_t)0x204e);
    NONFAILING(*(uint32_t*)0x20f4a004 = (uint32_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a008 = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a009 = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a00a = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a00b = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a00c = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a00d = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a00e = (uint8_t)0x0);
    NONFAILING(*(uint8_t*)0x20f4a00f = (uint8_t)0x0);
    r[35] = execute_syscall(__NR_connect, 0xfffffffffffffffful,
                            0x20f4a000ul, 0x10ul, 0, 0, 0, 0, 0, 0);
    break;
  case 5:
    NONFAILING(*(uint16_t*)0x20f4cfe0 = (uint16_t)0xa);
    NONFAILING(*(uint16_t*)0x20f4cfe2 = (uint16_t)0x204e);
    NONFAILING(*(uint32_t*)0x20f4cfe4 = (uint32_t)0x0);
    NONFAILING(*(uint64_t*)0x20f4cfe8 = (uint64_t)0x0);
    NONFAILING(*(uint64_t*)0x20f4cff0 = (uint64_t)0x100000000000000);
    NONFAILING(*(uint32_t*)0x20f4cff8 = (uint32_t)0x5);
    r[42] =
        execute_syscall(__NR_sendto, 0xfffffffffffffffful, 0x20006000ul,
                        0x0ul, 0x0ul, 0x20f4cfe0ul, 0x20ul, 0, 0, 0);
    break;
  case 6:
    r[43] = execute_syscall(__NR_recvfrom, 0xfffffffffffffffful,
                            0x20144f28ul, 0x0ul, 0x10000ul,
                            0x20f4e000ul, 0x0ul, 0, 0, 0);
    break;
  case 7:
    r[44] = execute_syscall(__NR_socket, 0x1ful, 0x5ul, 0x2ul, 0, 0, 0,
                            0, 0, 0);
    break;
  case 8:
    r[45] = execute_syscall(__NR_write, r[1], 0x20aa4fdaul, 0xfffful, 0,
                            0, 0, 0, 0, 0);
    break;
  case 9:
    NONFAILING(*(uint32_t*)0x20f54000 = (uint32_t)0x0);
    NONFAILING(*(uint32_t*)0x20f54004 = (uint32_t)0x0);
    NONFAILING(*(uint64_t*)0x20f54008 = (uint64_t)0x0);
    r[49] =
        execute_syscall(__NR_ioctl, 0xfffffffffffffffful, 0xc010640bul,
                        0x20f54000ul, 0, 0, 0, 0, 0, 0);
    break;
  case 10:
    NONFAILING(*(uint32_t*)0x20f54000 = (uint32_t)0x0);
    NONFAILING(*(uint32_t*)0x20f54004 = (uint32_t)0x0);
    NONFAILING(*(uint64_t*)0x20f54008 = (uint64_t)0xfc51);
    r[53] =
        execute_syscall(__NR_ioctl, 0xfffffffffffffffful, 0xc010640bul,
                        0x20f54000ul, 0, 0, 0, 0, 0, 0);
    break;
  case 11:
    NONFAILING(memcpy((void*)0x20f50fe1, "\x1f\x00\x00\x80\x01\x00\x00"
                                         "\x16\x00\x00\x00\x9a\xc7\x00"
                                         "\x00\x06",
                      16));
    r[55] = execute_syscall(__NR_write, r[1], 0x20f50fe1ul, 0x10ul, 0,
                            0, 0, 0, 0, 0);
    break;
  }
  return 0;
}

void loop()
{
  long i;
  pthread_t th[24];

  memset(r, -1, sizeof(r));
  srand(getpid());
  for (i = 0; i < 12; i++) {
    pthread_create(&th[i], 0, thr, (void*)i);
    usleep(10000);
  }
  for (i = 0; i < 12; i++) {
    pthread_create(&th[12 + i], 0, thr, (void*)i);
    if (rand() % 2)
      usleep(rand() % 10000);
  }
  usleep(100000);
}

int main()
{
  setup_main_process(0, false);
  int pid = do_sandbox_none();
  int status = 0;
  while (waitpid(pid, &status, __WALL) != pid) {
  }
  return 0;
}