Re: [syzbot] [overlayfs?] BUG: unable to handle kernel NULL pointer dereference in __lookup_slow (3)

[syzbot <syzbot+94891a5155abdf6821b7@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel NULL pointer dereference in __lookup_slow

loop0: detected capacity change from 0 to 64
overlayfs: fs on './file0' does not support file handles, falling back to index=off,nfs_export=off.
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 800000001f849067 P4D 800000001f849067 PUD 1fabf067 PMD 0 
Oops: Oops: 0010 [#1] PREEMPT SMP KASAN PTI
CPU: 0 UID: 0 PID: 6157 Comm: syz.0.15 Not tainted 6.11.0-rc5-syzkaller-00017-g7d6899fb69d2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc9000492f558 EFLAGS: 00010246
RAX: 1ffffffff17f1868 RBX: ffffffff8bf8c340 RCX: ffff888024845a00
RDX: 0000000000000000 RSI: ffff8880699ead38 RDI: ffff888069bac018
RBP: ffffc9000492f670 R08: ffffffff820c2f53 R09: 1ffffffff29ad1f5
R10: dffffc0000000000 R11: 0000000000000000 R12: dffffc0000000000
R13: ffff8880699ead38 R14: 1ffff1100d33d5a7 R15: 1ffff92000925eb0
FS:  00007f735e4b46c0(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000078faa000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __lookup_slow+0x28c/0x3f0 fs/namei.c:1718
 lookup_slow fs/namei.c:1735 [inline]
 lookup_one_unlocked+0x1a4/0x290 fs/namei.c:2898
 ovl_lookup_positive_unlocked fs/overlayfs/namei.c:210 [inline]
 ovl_lookup_single+0x200/0xbd0 fs/overlayfs/namei.c:240
 ovl_lookup_layer+0x417/0x510 fs/overlayfs/namei.c:333
 ovl_lookup+0xcf7/0x2a60 fs/overlayfs/namei.c:1124
 lookup_one_qstr_excl+0x11f/0x260 fs/namei.c:1633
 filename_create+0x297/0x540 fs/namei.c:3980
 do_mknodat+0x18b/0x5b0 fs/namei.c:4125
 __do_sys_mknod fs/namei.c:4171 [inline]
 __se_sys_mknod fs/namei.c:4169 [inline]
 __x64_sys_mknod+0x8c/0xa0 fs/namei.c:4169
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f735d779ef9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f735e4b4038 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
RAX: ffffffffffffffda RBX: 00007f735d915f80 RCX: 00007f735d779ef9
RDX: 0000000000000700 RSI: 0000000000002000 RDI: 0000000020000140
RBP: 00007f735d7e793e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f735d915f80 R15: 00007ffd8cecbb18
 </TASK>
Modules linked in:
CR2: 0000000000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc9000492f558 EFLAGS: 00010246
RAX: 1ffffffff17f1868 RBX: ffffffff8bf8c340 RCX: ffff888024845a00
RDX: 0000000000000000 RSI: ffff8880699ead38 RDI: ffff888069bac018
RBP: ffffc9000492f670 R08: ffffffff820c2f53 R09: 1ffffffff29ad1f5
R10: dffffc0000000000 R11: 0000000000000000 R12: dffffc0000000000
R13: ffff8880699ead38 R14: 1ffff1100d33d5a7 R15: 1ffff92000925eb0
FS:  00007f735e4b46c0(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000078faa000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


Tested on:

commit:         7d6899fb ovl: fsync after metadata copy-up
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs.git overlayfs-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1272d5b7980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d806687521800cad
dashboard link: https://syzkaller.appspot.com/bug?extid=94891a5155abdf6821b7
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.