KASAN: stack-out-of-bounds Read in __aa_lookupn_ns

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    02214bfc89c7 Merge tag 'media/v4.19-2' of git://git.kernel..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=159b85f1400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=22a62640793a83c9
dashboard link: https://syzkaller.appspot.com/bug?extid=61e4b490d9d2da591b50
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1782443a400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15ebf556400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+61e4b490d9d2da591b50 at syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in memcmp+0xe3/0x160 lib/string.c:861
Read of size 1 at addr ffff8801ba8df400 by task syz-executor610/5662

CPU: 0 PID: 5662 Comm: syz-executor610 Not tainted 4.19.0-rc5+ #252
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+0x1c4/0x2b4 lib/dump_stack.c:113
  print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
  __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
  memcmp+0xe3/0x160 lib/string.c:861
  strnstr+0x4b/0x70 lib/string.c:934
  __aa_lookupn_ns+0xc1/0x570 security/apparmor/policy_ns.c:209
  aa_lookupn_ns+0x88/0x1e0 security/apparmor/policy_ns.c:240
  aa_fqlookupn_profile+0x1b9/0x1010 security/apparmor/policy.c:468
  fqlookupn_profile+0x80/0xc0 security/apparmor/label.c:1844
  aa_label_strn_parse+0xa3a/0x1230 security/apparmor/label.c:1908
  aa_label_parse+0x42/0x50 security/apparmor/label.c:1943
  aa_change_profile+0x513/0x3510 security/apparmor/domain.c:1362
  apparmor_setprocattr+0xaa4/0x1150 security/apparmor/lsm.c:658
  security_setprocattr+0x66/0xc0 security/security.c:1298
  proc_pid_attr_write+0x301/0x540 fs/proc/base.c:2555
  __vfs_write+0x119/0x9f0 fs/read_write.c:485
  vfs_write+0x1fc/0x560 fs/read_write.c:549
  ksys_write+0x101/0x260 fs/read_write.c:598
  __do_sys_write fs/read_write.c:610 [inline]
  __se_sys_write fs/read_write.c:607 [inline]
  __x64_sys_write+0x73/0xb0 fs/read_write.c:607
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441469
Code: e8 cc b2 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 4b 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffced82b788 EFLAGS: 00000213 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441469
RDX: 0000000000000009 RSI: 0000000020000180 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000001e49880 R11: 0000000000000213 R12: 000000000000014f
R13: 000000000000ae37 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea0006ea37c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 ffffffff06ea0101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801ba8df300: f2 f2 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffff8801ba8df380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1
> ffff8801ba8df400: f1 f1 f1 f8 f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f2
                    ^
  ffff8801ba8df480: f2 f2 f2 f8 f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f2
  ffff8801ba8df500: f2 f2 f2 00 00 00 00 00 00 00 00 f3 f3 f3 f3 00
==================================================================


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