Re: general protection fault in ovl_free_fs

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    d7b686ebf704 Merge branch 'i2c/for-current' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=148ac149400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8f59875069d721b6
dashboard link: https://syzkaller.appspot.com/bug?extid=c75f181dc8429d2eb887
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11553b7a400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14b16421400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c75f181dc8429d2eb887@xxxxxxxxxxxxxxxxxxxxxxxxx

R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
overlayfs: failed to clone upperpath
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 5473 Comm: syz-executor554 Not tainted 4.19.0-rc2+ #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:ovl_free_fs+0x504/0x690 fs/overlayfs/super.c:226
Code: 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 78 01 00 00 48  
b8 00 00 00 00 00 fc ff df 4c 8b 23 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 0f  
85 67 01 00 00 49 8b 3c 24 e8 c9 0a 01 00 e9 0c fc
RSP: 0018:ffff8801b3de7798 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8801d87b7800 RCX: ffffffff828cacaf
RDX: 0000000000000000 RSI: ffffffff828cb065 RDI: 0000000000000001
RBP: ffff8801b3de77f0 R08: ffff8801c44ba680 R09: ffffed003b5e4732
R10: ffffed003b5e4732 R11: ffff8801daf23993 R12: 0000000000000000
R13: ffff8801d87b7820 R14: fffffffffffffff4 R15: ffff8801d87b7800
FS:  000000000207a880(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f14a574e169 CR3: 00000001c5068000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 ovl_fill_super+0x4f4/0x40a3 fs/overlayfs/super.c:1508
 mount_nodev+0x6b/0x110 fs/super.c:1204
 ovl_mount+0x2c/0x40 fs/overlayfs/super.c:1516
 mount_fs+0xae/0x31d fs/super.c:1261
 vfs_kern_mount.part.35+0xdc/0x4f0 fs/namespace.c:961
 vfs_kern_mount fs/namespace.c:951 [inline]
 do_new_mount fs/namespace.c:2457 [inline]
 do_mount+0x581/0x31f0 fs/namespace.c:2787
 ksys_mount+0x12d/0x140 fs/namespace.c:3003
 __do_sys_mount fs/namespace.c:3017 [inline]
 __se_sys_mount fs/namespace.c:3014 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3014
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x445119
Code: ad ce 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 7b ce fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffef77a0948 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000445119
RDX: 00000000200000c0 RSI: 0000000020000080 RDI: 0000000000000000
RBP: 00007ffef77a0960 R08: 0000000020000100 R09: 00007ffef77f92f4
R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 6b50ff34ce671ab8 ]---
RIP: 0010:ovl_free_fs+0x504/0x690 fs/overlayfs/super.c:226
Code: 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 78 01 00 00 48  
b8 00 00 00 00 00 fc ff df 4c 8b 23 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 0f  
85 67 01 00 00 49 8b 3c 24 e8 c9 0a 01 00 e9 0c fc
RSP: 0018:ffff8801b3de7798 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8801d87b7800 RCX: ffffffff828cacaf
RDX: 0000000000000000 RSI: ffffffff828cb065 RDI: 0000000000000001
RBP: ffff8801b3de77f0 R08: ffff8801c44ba680 R09: ffffed003b5e4732
R10: ffffed003b5e4732 R11: ffff8801daf23993 R12: 0000000000000000
R13: ffff8801d87b7820 R14: fffffffffffffff4 R15: ffff8801d87b7800
FS:  000000000207a880(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f14a574e169 CR3: 00000001c5068000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400