[syzbot] KASAN: use-after-free Read in ovl_real_fdget_meta

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 92f791eb Add linux-next specific files for 20210302
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12696076d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=55e0d976097c2fbd
dashboard link: https://syzkaller.appspot.com/bug?extid=d8f10499005854b34b80

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d8f104...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in file_inode include/linux/fs.h:1301 [inline]
BUG: KASAN: use-after-free in ovl_real_fdget_meta+0x482/0x500 fs/overlayfs/file.c:118
Read of size 8 at addr ffff88801854d420 by task syz-executor.2/18364

CPU: 0 PID: 18364 Comm: syz-executor.2 Not tainted 5.12.0-rc1-next-20210302-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0xfa/0x151 lib/dump_stack.c:120
print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:232
__kasan_report mm/kasan/report.c:399 [inline]
kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:416
file_inode include/linux/fs.h:1301 [inline]
ovl_real_fdget_meta+0x482/0x500 fs/overlayfs/file.c:118
ovl_real_fdget+0xad/0x260 fs/overlayfs/file.c:141
ovl_flush+0x72/0x230 fs/overlayfs/file.c:695
filp_close+0xb4/0x170 fs/open.c:1295
close_fd+0x5c/0x80 fs/file.c:628
__do_sys_close fs/open.c:1314 [inline]
__se_sys_close fs/open.c:1312 [inline]
__x64_sys_close+0x2f/0xa0 fs/open.c:1312
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x41920b
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:00007fffbf66ec90 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000041920b
RDX: 0000000000570448 RSI: ffffffff8906c86e RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000001b2c13ba84
R10: 00007fffbf66ed80 R11: 0000000000000293 R12: 000000000005a429
R13: 00000000000003e8 R14: 000000000056bf60 R15: 000000000005a36d

Allocated by task 18368:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:427 [inline]
__kasan_slab_alloc+0x75/0x90 mm/kasan/common.c:460
kasan_slab_alloc include/linux/kasan.h:223 [inline]
slab_post_alloc_hook mm/slab.h:516 [inline]
slab_alloc_node mm/slub.c:2907 [inline]
slab_alloc mm/slub.c:2915 [inline]
kmem_cache_alloc+0x15e/0x380 mm/slub.c:2920
kmem_cache_zalloc include/linux/slab.h:674 [inline]
__alloc_file+0x21/0x280 fs/file_table.c:101
alloc_empty_file_noaccount+0x19/0x90 fs/file_table.c:172
open_with_fake_path+0x27/0xe0 fs/open.c:969
ovl_open_realfile+0x270/0x2f0 fs/overlayfs/file.c:60
ovl_open fs/overlayfs/file.c:156 [inline]
ovl_open+0x125/0x270 fs/overlayfs/file.c:144
do_dentry_open+0x4b9/0x11b0 fs/open.c:826
do_open fs/namei.c:3365 [inline]
path_openat+0x1c0e/0x27e0 fs/namei.c:3498
do_filp_open+0x17e/0x3c0 fs/namei.c:3525
do_sys_openat2+0x16d/0x420 fs/open.c:1187
do_sys_open fs/open.c:1203 [inline]
__do_sys_openat fs/open.c:1219 [inline]
__se_sys_openat fs/open.c:1214 [inline]
__x64_sys_openat+0x13f/0x1f0 fs/open.c:1214
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 4854:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:357
____kasan_slab_free mm/kasan/common.c:360 [inline]
____kasan_slab_free mm/kasan/common.c:325 [inline]
__kasan_slab_free+0xf5/0x130 mm/kasan/common.c:367
kasan_slab_free include/linux/kasan.h:199 [inline]
slab_free_hook mm/slub.c:1562 [inline]
slab_free_freelist_hook+0x72/0x1b0 mm/slub.c:1600
slab_free mm/slub.c:3161 [inline]
kmem_cache_free+0x8b/0x730 mm/slub.c:3177
rcu_do_batch kernel/rcu/tree.c:2559 [inline]
rcu_core+0x722/0x1280 kernel/rcu/tree.c:2794
__do_softirq+0x29b/0x9f6 kernel/softirq.c:345

Last potentially related work creation:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:345
__call_rcu kernel/rcu/tree.c:3039 [inline]
call_rcu+0xb1/0x700 kernel/rcu/tree.c:3114
task_work_run+0xdd/0x1a0 kernel/task_work.c:140
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:208
__syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x44/0xae

Second to last potentially related work creation:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:345
__call_rcu kernel/rcu/tree.c:3039 [inline]
call_rcu+0xb1/0x700 kernel/rcu/tree.c:3114
task_work_run+0xdd/0x1a0 kernel/task_work.c:140
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:208
__syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff88801854d400
which belongs to the cache filp of size 464
The buggy address is located 32 bytes inside of
464-byte region [ffff88801854d400, ffff88801854d5d0)
The buggy address belongs to the page:
page:000000004db6be2d refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1854c
head:000000004db6be2d order:1 compound_mapcount:0
flags: 0xfff00000010200(slab|head)
raw: 00fff00000010200 ffffea0000bff380 0000000600000006 ffff888140005500
raw: 0000000000000000 00000000000c000c 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88801854d300: fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc
ffff88801854d380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801854d400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88801854d480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88801854d500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.