On Wed, Jan 30, 2019 at 10:30 PM Paul Moore [off-list ref] wrote:

On Wed, Jan 30, 2019 at 4:01 PM syzbot
[off-list ref] wrote:

quoted

Hello,

syzbot found the following crash on:

HEAD commit:    62967898789d Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=167fdef8c00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4fceea9e2d99ac20
dashboard link: https://syzkaller.appspot.com/bug?extid=1bfc00ca3aabe5bcd4cb
compiler:       gcc (GCC) 9.0.0 20181231 (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: syzbot+1bfc00ca3aabe5bcd4cb@syzkaller.appspotmail.com

8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KASAN: use-after-free in selinux_netlbl_socket_setsockopt+0x49b/0x510
security/selinux/netlabel.c:525
Read of size 8 at addr ffff8880a63cf078 by task syz-executor3/18477

CPU: 1 PID: 18477 Comm: syz-executor3 Not tainted 5.0.0-rc4+ #51
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+0x1db/0x2d0 lib/dump_stack.c:113
  print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
  kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
  selinux_netlbl_socket_setsockopt+0x49b/0x510
security/selinux/netlabel.c:525

At first glance this seems odd.  The line above is simply
dereferencing sock->sk_security (getting the "sksec"), which we also
do higher up selinux_socket_setsockopt() via sock_has_perm().  Unless
somehow the socket is being released/freed in the middle of a
setsockopt() syscall this looks like maybe it's something else?

Hi Paul,

Searching for af_netrom across other syzbot bugs:
https://groups.google.com/forum/#!searchin/syzkaller-bugs/af_netrom%7Csort:date

I see at least:
https://syzkaller.appspot.com/bug?extid=b0b1952f5864b4009b09
https://syzkaller.appspot.com/bug?extid=febf3c50d4262e578b1c
https://syzkaller.appspot.com/bug?extid=defa700d16f1bd1b9a05

Which suggests there are some serious lifetime problems in netrom
sockets. That would probably explain this crash as well.

+netrom maintainers, does this explanation look plausible to you?
should we dup this crash onto one of the other netrom bugs? and
perhaps these netrom bugs across themselves too?

quoted

  selinux_socket_setsockopt+0x67/0x90 security/selinux/hooks.c:4693
  security_socket_setsockopt+0x7d/0xc0 security/security.c:1467
  __sys_setsockopt+0xe4/0x3a0 net/socket.c:1892
  __do_sys_setsockopt net/socket.c:1913 [inline]
  __se_sys_setsockopt net/socket.c:1910 [inline]
  __x64_sys_setsockopt+0xbe/0x150 net/socket.c:1910
  do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458089
Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb988b9cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000458089
RDX: 0000000000000078 RSI: 0000000000000084 RDI: 000000000000000a
RBP: 000000000073c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb988b9d6d4
R13: 00000000004cc9e8 R14: 00000000004da6a8 R15: 00000000ffffffff

Allocated by task 18471:
  save_stack+0x45/0xd0 mm/kasan/common.c:73
  set_track mm/kasan/common.c:85 [inline]
  __kasan_kmalloc mm/kasan/common.c:496 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:469
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:504
  __do_kmalloc mm/slab.c:3711 [inline]
  __kmalloc+0x15c/0x740 mm/slab.c:3720
  kmalloc include/linux/slab.h:550 [inline]
  sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1477
  sk_alloc+0xd7/0x1690 net/core/sock.c:1531
  nr_create+0xb9/0x5e0 net/netrom/af_netrom.c:436
  __sock_create+0x532/0x930 net/socket.c:1277
  sock_create net/socket.c:1317 [inline]
  __sys_socket+0x106/0x260 net/socket.c:1347
  __do_sys_socket net/socket.c:1356 [inline]
  __se_sys_socket net/socket.c:1354 [inline]
  __x64_sys_socket+0x73/0xb0 net/socket.c:1354
  do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 18466:
  save_stack+0x45/0xd0 mm/kasan/common.c:73
  set_track mm/kasan/common.c:85 [inline]
  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:458
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:466
  __cache_free mm/slab.c:3487 [inline]
  kfree+0xcf/0x230 mm/slab.c:3806
  sk_prot_free net/core/sock.c:1514 [inline]
  __sk_destruct+0x76d/0xa60 net/core/sock.c:1596
  sk_destruct+0x7b/0x90 net/core/sock.c:1604
  __sk_free+0xce/0x300 net/core/sock.c:1615
  sk_free+0x42/0x50 net/core/sock.c:1626
  sock_put include/net/sock.h:1707 [inline]
  nr_release+0x337/0x3c0 net/netrom/af_netrom.c:557
  __sock_release+0xd3/0x250 net/socket.c:579
  sock_close+0x1b/0x30 net/socket.c:1141
  __fput+0x3c5/0xb10 fs/file_table.c:278
  ____fput+0x16/0x20 fs/file_table.c:309
  task_work_run+0x1f4/0x2b0 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
  exit_to_usermode_loop+0x32a/0x3b0 arch/x86/entry/common.c:166
  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
  do_syscall_64+0x696/0x800 arch/x86/entry/common.c:293
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a63cec80
  which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1016 bytes inside of
  2048-byte region [ffff8880a63cec80, ffff8880a63cf480)
The buggy address belongs to the page:
page:ffffea000298f380 count:1 mapcount:0 mapping:ffff88812c3f0c40 index:0x0
compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea000127f888 ffffea00013a3188 ffff88812c3f0c40
raw: 0000000000000000 ffff8880a63ce400 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8880a63cef00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880a63cef80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

quoted

ffff8880a63cf000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

                                                                 ^
  ffff8880a63cf080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880a63cf100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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--
paul moore
www.paul-moore.com