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Date:   Tue, 13 Nov 2018 11:58:03 -0800
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Subject: Re: KASAN: use-after-free Read in locks_delete_block
From:   syzbot <syzbot+a4a3d526b4157113ec6a@syzkaller.appspotmail.com>
To:     bfields@fieldses.org, jlayton@kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        neilb@suse.de, syzkaller-bugs@googlegroups.com,
        viro@zeniv.linux.org.uk
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syzbot has found a reproducer for the following crash on:

HEAD commit:    442b8cea2477 Add linux-next specific files for 20181109
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12fbd905400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2f72bdb11df9fbe8
dashboard link: https://syzkaller.appspot.com/bug?extid=a4a3d526b4157113ec6a
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10480d33400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a4a3d526b4157113ec6a@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in __list_del_entry_valid+0xf1/0x100  
lib/list_debug.c:51
Read of size 8 at addr ffff8801b27c7c70 by task syz-executor0/6767

CPU: 1 PID: 6767 Comm: syz-executor0 Not tainted 4.20.0-rc1-next-20181109+  
#110
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
  print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
  __list_del_entry_valid+0xf1/0x100 lib/list_debug.c:51
  __list_del_entry include/linux/list.h:117 [inline]
  list_del_init include/linux/list.h:159 [inline]
  __locks_delete_block fs/locks.c:683 [inline]
  locks_delete_block+0xce/0x3d0 fs/locks.c:716
  locks_mandatory_area+0x48b/0x6a0 fs/locks.c:1398
  locks_verify_truncate include/linux/fs.h:2361 [inline]
  do_sys_ftruncate+0x4b2/0x550 fs/open.c:190
  __do_sys_ftruncate fs/open.c:204 [inline]
  __se_sys_ftruncate fs/open.c:202 [inline]
  __x64_sys_ftruncate+0x59/0x80 fs/open.c:202
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f4319e97c78 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 0000000000000039 RDI: 0000000000000004
RBP: 000000000072c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f4319e986d4
R13: 00000000004bde51 R14: 00000000004cd048 R15: 00000000ffffffff

The buggy address belongs to the page:
page:ffffea0006c9f1c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 ffffffff06c90101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801b27c7b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
  ffff8801b27c7b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff8801b27c7c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                              ^
  ffff8801b27c7c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
  ffff8801b27c7d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================