Subject: KASAN: use-after-free Read in refcount_sub_and_test

From: syzbot <[email-masked]>
Date: Tue, 31 Jul 2018 01:22:02 -0700

Hello,

syzbot found the following crash on:

HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=16ed5cf0400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
dashboard link: https://syzkaller.appspot.com/bug?extid=8c17db54fd0c0a2ee849
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

device lo left promiscuous mode
==================================================================
BUG: KASAN: use-after-free in atomic_read  
include/asm-generic/atomic-instrumented.h:21 [inline]
BUG: KASAN: use-after-free in refcount_sub_and_test+0x9a/0x350  
lib/refcount.c:179
Read of size 4 at addr ffff8801d96d2844 by task syz-executor1/4479

CPU: 0 PID: 4479 Comm: syz-executor1 Not tainted 4.18.0-rc6+ #34
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+0x1c9/0x2b4 lib/dump_stack.c:113
  print_address_description+0x6c/0x20b mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
  check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
  kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272
  atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
  refcount_sub_and_test+0x9a/0x350 lib/refcount.c:179
  refcount_dec_and_test+0x1a/0x20 lib/refcount.c:212
  fib6_metrics_release+0x4f/0x90 net/ipv6/ip6_fib.c:178
  fib6_drop_pcpu_from net/ipv6/ip6_fib.c:899 [inline]
  fib6_purge_rt+0x5ec/0x7f0 net/ipv6/ip6_fib.c:934
  fib6_del_route net/ipv6/ip6_fib.c:1784 [inline]
  fib6_del+0xc11/0x1310 net/ipv6/ip6_fib.c:1815
  fib6_clean_node+0x3ee/0x5e0 net/ipv6/ip6_fib.c:1976
  fib6_walk_continue+0x4b1/0x8e0 net/ipv6/ip6_fib.c:1899
  fib6_walk+0x95/0xf0 net/ipv6/ip6_fib.c:1947
  fib6_clean_tree+0x1ea/0x360 net/ipv6/ip6_fib.c:2024
  __fib6_clean_all+0x21c/0x420 net/ipv6/ip6_fib.c:2040
  fib6_clean_all+0x27/0x30 net/ipv6/ip6_fib.c:2051
  rt6_sync_down_dev net/ipv6/route.c:4083 [inline]
  rt6_disable_ip+0x111/0x7e0 net/ipv6/route.c:4088
  addrconf_ifdown+0x16f/0x1670 net/ipv6/addrconf.c:3650
  addrconf_notify+0x6e9/0x27f0 net/ipv6/addrconf.c:3575
  notifier_call_chain+0x180/0x390 kernel/notifier.c:93
  __raw_notifier_call_chain kernel/notifier.c:394 [inline]
  raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
  call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1735
  call_netdevice_notifiers net/core/dev.c:1753 [inline]
  dev_close_many+0x447/0x8d0 net/core/dev.c:1505
  rollback_registered_many+0x52b/0xef0 net/core/dev.c:7452
  rollback_registered+0x1e9/0x420 net/core/dev.c:7517
  unregister_netdevice_queue+0x32f/0x660 net/core/dev.c:8561
  unregister_netdevice include/linux/netdevice.h:2548 [inline]
  __tun_detach+0x11d1/0x15e0 drivers/net/tun.c:727
  tun_detach drivers/net/tun.c:744 [inline]
  tun_chr_close+0xe3/0x180 drivers/net/tun.c:3271
  __fput+0x355/0x8b0 fs/file_table.c:209
  ____fput+0x15/0x20 fs/file_table.c:243
  task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
  exit_task_work include/linux/task_work.h:22 [inline]
  do_exit+0x1b08/0x2750 kernel/exit.c:865
  do_group_exit+0x177/0x440 kernel/exit.c:968
  __do_sys_exit_group kernel/exit.c:979 [inline]
  __se_sys_exit_group kernel/exit.c:977 [inline]
  __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:977
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x456a09
Code: Bad RIP value.
RSP: 002b:00007fffa8ff4908 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000456a09
RDX: 00000000004104e0 RSI: 0000000000a44bd0 RDI: 0000000000000045
RBP: 00000000004c1904 R08: 000000000000000b R09: 0000000000000000
R10: 0000000001445940 R11: 0000000000000246 R12: 0000000001446940
R13: 0000000000000000 R14: 000000000000057e R15: badc0ffeebadface

Allocated by task 28651:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
  set_track mm/kasan/kasan.c:460 [inline]
  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
  kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620
  kmalloc include/linux/slab.h:513 [inline]
  kzalloc include/linux/slab.h:707 [inline]
  fib6_metric_set+0x163/0x2c0 net/ipv6/ip6_fib.c:645
  fib6_add_rt2node+0xe36/0x27f0 net/ipv6/ip6_fib.c:1000
  fib6_add+0xaae/0x14d0 net/ipv6/ip6_fib.c:1308
  __ip6_ins_rt+0x54/0x80 net/ipv6/route.c:1163
  ip6_route_add+0x6d/0xc0 net/ipv6/route.c:3171
  addrconf_prefix_route.isra.48+0x51d/0x720 net/ipv6/addrconf.c:2347
  inet6_addr_modify net/ipv6/addrconf.c:4627 [inline]
  inet6_rtm_newaddr+0x112e/0x1b50 net/ipv6/addrconf.c:4743
  rtnetlink_rcv_msg+0x46e/0xc30 net/core/rtnetlink.c:4665
  netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2453
  rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4683
  netlink_unicast_kernel net/netlink/af_netlink.c:1315 [inline]
  netlink_unicast+0x5a0/0x760 net/netlink/af_netlink.c:1341
  netlink_sendmsg+0xa18/0xfd0 net/netlink/af_netlink.c:1906
  sock_sendmsg_nosec net/socket.c:642 [inline]
  sock_sendmsg+0xd5/0x120 net/socket.c:652
  ___sys_sendmsg+0x7fd/0x930 net/socket.c:2126
  __sys_sendmsg+0x11d/0x290 net/socket.c:2164
  __do_sys_sendmsg net/socket.c:2173 [inline]
  __se_sys_sendmsg net/socket.c:2171 [inline]
  __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2171
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 4479:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
  set_track mm/kasan/kasan.c:460 [inline]
  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
  __cache_free mm/slab.c:3498 [inline]
  kfree+0xd9/0x260 mm/slab.c:3813
  fib6_metrics_release+0x77/0x90 net/ipv6/ip6_fib.c:179
  fib6_drop_pcpu_from net/ipv6/ip6_fib.c:899 [inline]
  fib6_purge_rt+0x5ec/0x7f0 net/ipv6/ip6_fib.c:934
  fib6_del_route net/ipv6/ip6_fib.c:1784 [inline]
  fib6_del+0xc11/0x1310 net/ipv6/ip6_fib.c:1815
  fib6_clean_node+0x3ee/0x5e0 net/ipv6/ip6_fib.c:1976
  fib6_walk_continue+0x4b1/0x8e0 net/ipv6/ip6_fib.c:1899
  fib6_walk+0x95/0xf0 net/ipv6/ip6_fib.c:1947
  fib6_clean_tree+0x1ea/0x360 net/ipv6/ip6_fib.c:2024
  __fib6_clean_all+0x21c/0x420 net/ipv6/ip6_fib.c:2040
  fib6_clean_all+0x27/0x30 net/ipv6/ip6_fib.c:2051
  rt6_sync_down_dev net/ipv6/route.c:4083 [inline]
  rt6_disable_ip+0x111/0x7e0 net/ipv6/route.c:4088
  addrconf_ifdown+0x16f/0x1670 net/ipv6/addrconf.c:3650
  addrconf_notify+0x6e9/0x27f0 net/ipv6/addrconf.c:3575
  notifier_call_chain+0x180/0x390 kernel/notifier.c:93
  __raw_notifier_call_chain kernel/notifier.c:394 [inline]
  raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
  call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1735
  call_netdevice_notifiers net/core/dev.c:1753 [inline]
  dev_close_many+0x447/0x8d0 net/core/dev.c:1505
  rollback_registered_many+0x52b/0xef0 net/core/dev.c:7452
  rollback_registered+0x1e9/0x420 net/core/dev.c:7517
  unregister_netdevice_queue+0x32f/0x660 net/core/dev.c:8561
  unregister_netdevice include/linux/netdevice.h:2548 [inline]
  __tun_detach+0x11d1/0x15e0 drivers/net/tun.c:727
  tun_detach drivers/net/tun.c:744 [inline]
  tun_chr_close+0xe3/0x180 drivers/net/tun.c:3271
  __fput+0x355/0x8b0 fs/file_table.c:209
  ____fput+0x15/0x20 fs/file_table.c:243
  task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
  exit_task_work include/linux/task_work.h:22 [inline]
  do_exit+0x1b08/0x2750 kernel/exit.c:865
  do_group_exit+0x177/0x440 kernel/exit.c:968
  __do_sys_exit_group kernel/exit.c:979 [inline]
  __se_sys_exit_group kernel/exit.c:977 [inline]
  __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:977
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801d96d2800
  which belongs to the cache kmalloc-96 of size 96
The buggy address is located 68 bytes inside of
  96-byte region [ffff8801d96d2800, ffff8801d96d2860)
The buggy address belongs to the page:
page:ffffea000765b480 count:1 mapcount:0 mapping:ffff8801dac004c0  
index:0xffff8801d96d2700
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006c46348 ffffea0006d0d288 ffff8801dac004c0
raw: ffff8801d96d2700 ffff8801d96d2000 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801d96d2700: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
  ffff8801d96d2780: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ffff8801d96d2800: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                                            ^
  ffff8801d96d2880: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
  ffff8801d96d2900: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
==================================================================

---
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