KASAN: use-after-free Read in class_equal

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    c50bbf61 Merge tag 'platform-drivers-x86-v5.2-2' of git://..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12130c9aa00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fc045131472947d7
dashboard link: https://syzkaller.appspot.com/bug?extid=83c135be90fc92db7e13
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12e7d84ca00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+83c135be90fc92db7e13@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in class_equal+0x40/0x50  
kernel/locking/lockdep.c:1527
Read of size 8 at addr ffff88807aedf360 by task syz-executor.0/9275

CPU: 0 PID: 9275 Comm: syz-executor.0 Not tainted 5.2.0-rc1+ #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:

Allocated by task 9264:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_kmalloc mm/kasan/common.c:489 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
 slab_post_alloc_hook mm/slab.h:437 [inline]
 slab_alloc mm/slab.c:3326 [inline]
 kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3488
 getname_flags fs/namei.c:138 [inline]
 getname_flags+0xd6/0x5b0 fs/namei.c:128
 getname+0x1a/0x20 fs/namei.c:209
 do_sys_open+0x2c9/0x5d0 fs/open.c:1064
 __do_sys_open fs/open.c:1088 [inline]
 __se_sys_open fs/open.c:1083 [inline]
 __x64_sys_open+0x7e/0xc0 fs/open.c:1083
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9264:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
 __cache_free mm/slab.c:3432 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3698
 putname+0xef/0x130 fs/namei.c:259
 do_sys_open+0x318/0x5d0 fs/open.c:1079
 __do_sys_open fs/open.c:1088 [inline]
 __se_sys_open fs/open.c:1083 [inline]
 __x64_sys_open+0x7e/0xc0 fs/open.c:1083
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88807aede580
 which belongs to the cache names_cache of size 4096
The buggy address is located 3552 bytes inside of
 4096-byte region [ffff88807aede580, ffff88807aedf580)
The buggy address belongs to the page:
page:ffffea0001ebb780 refcount:1 mapcount:0 mapping:ffff8880aa596c40  
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0001ebb708 ffffea0001ebb908 ffff8880aa596c40
raw: 0000000000000000 ffff88807aede580 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88807aedf200: 00 00 fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807aedf280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb f1 f1
> ffff88807aedf300: f1 f1 00 f2 f2 f2 00 f2 f2 f2 fb fb fb fb 00 00
                                                       ^
 ffff88807aedf380: 00 f3 f3 f3 f3 f3 fb fb fb fb fb fb fb fb fb fb
 ffff88807aedf400: fb fb fb fb fb fb fb fb fb fb fb fb fb 00 00 00
==================================================================


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