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

[syzbot <syzbot+d3ed975648421c381ca4@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    358be656406d selftests/net: add txring_overwrite
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=113f8ed5400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c36a72af2123e78a
dashboard link: https://syzkaller.appspot.com/bug?extid=d3ed975648421c381ca4
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: syzbot+d3ed975648421c381ca4@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in atomic_read  
include/asm-generic/atomic-instrumented.h:21 [inline]
BUG: KASAN: stack-out-of-bounds in refcount_sub_and_test_checked+0x9d/0x310  
lib/refcount.c:179
Read of size 4 at addr ffff8881da9c0bf0 by task udevd/15453

CPU: 1 PID: 15453 Comm: udevd Not tainted 4.20.0-rc3+ #313
PANIC: double fault, error_code: 0x0
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+0x244/0x39d lib/dump_stack.c:113
CPU: 0 PID: 18956 Comm: syz-executor1 Not tainted 4.20.0-rc3+ #313
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:__udp4_lib_lookup+0x25/0x870 net/ipv4/udp.c:466
Code: ff 0f 1f 40 00 55 48 89 e5 41 57 41 56 41 55 49 bd 00 00 00 00 00 fc  
ff df 41 54 53 44 89 c3 48 81 ec 00 01 00 00 48 8b 45 20 <48> 89 bd 28 ff  
ff ff 66 c1 c3 08 4c 8b 65 18 89 b5 1c ff ff ff 89
  print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
RSP: 0018:ffff8881d9a8af98 EFLAGS: 00010282
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
RAX: 0000000000000000 RBX: 000000000000e5be RCX: 00000000111414ac
RDX: 000000000000224e RSI: 00000000aa1414ac RDI: ffff88818b3fc340
  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
  check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
RBP: ffff8881d9a8b0c0 R08: 000000000000e5be R09: 0000000000000001
  kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272
R10: 0000000000000000 R11: ffff8881dae2db3b R12: ffff8881d7835800
  atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
  refcount_sub_and_test_checked+0x9d/0x310 lib/refcount.c:179
R13: dffffc0000000000 R14: ffff8881d78357ec R15: 0000000000000003
FS:  00007f18ebe99700(0000) GS:ffff8881dae00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff8881d9a8af88 CR3: 000000014f1a9000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  refcount_dec_and_test_checked+0x1a/0x20 lib/refcount.c:212
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  kref_put include/linux/kref.h:69 [inline]
  aa_put_label security/apparmor/include/label.h:447 [inline]
  aa_free_file_ctx security/apparmor/include/file.h:75 [inline]
  apparmor_file_free_security+0x115/0x1a0 security/apparmor/lsm.c:450
Call Trace:


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