[syzbot] [nilfs?] general protection fault in __d_unalias

[syzbot <syzbot+ab57f676a518849a8d57@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    69b8923f5003 Merge tag 'for-linus-6.14-ofs4' of git://git...
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=14fbdddf980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=57ab43c279fa614d
dashboard link: https://syzkaller.appspot.com/bug?extid=ab57f676a518849a8d57
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15da95f8580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=165f8b24580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ea84ac864e92/disk-69b8923f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6a465997b4e0/vmlinux-69b8923f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d72b67b2bd15/bzImage-69b8923f.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/7d96d510aa23/mount_0.gz

The issue was bisected to:

commit 30d61efe118cad1a73ad2ad66a3298e4abdf9f41
Author: Al Viro <viro@zeniv.linux.org.uk>
Date:   Mon Jan 6 02:33:17 2025 +0000

    9p: fix ->rename_sem exclusion

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=148b7b64580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=168b7b64580000
console output: https://syzkaller.appspot.com/x/log.txt?x=128b7b64580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ab57f676a518849a8d57@syzkaller.appspotmail.com
Fixes: 30d61efe118c ("9p: fix ->rename_sem exclusion")

Oops: general protection fault, probably for non-canonical address 0xdffffc000000000d: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f]
CPU: 0 UID: 0 PID: 5821 Comm: syz-executor287 Not tainted 6.13.0-syzkaller-09793-g69b8923f5003 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
RIP: 0010:__d_unalias+0x199/0x2a0 fs/dcache.c:2969
Code: 98 00 00 00 4c 89 fb 48 c1 eb 03 49 89 ed 80 3c 2b 00 74 08 4c 89 ff e8 65 62 e7 ff 49 8b 2f 48 83 c5 68 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 48 62 e7 ff 4c 8b 5d 00 4d 85 db
RSP: 0018:ffffc90003d9fa98 EFLAGS: 00010202
RAX: 000000000000000d RBX: 1ffff1100996cb61 RCX: ffff88804d821e00
RDX: 0000000000000000 RSI: ffff88804cb65a70 RDI: ffff88804cb658f8
RBP: 0000000000000068 R08: ffff88804e530f6b R09: 1ffff11009ca61ed
R10: dffffc0000000000 R11: ffffed1009ca61ee R12: ffff88804cb65a70
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88804cb65b08
FS:  000055555b892380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe074ff000 CR3: 0000000078440000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 d_splice_alias+0x1e6/0x330 fs/dcache.c:3037
 nilfs_lookup+0x1c2/0x2a0 fs/nilfs2/namei.c:77
 lookup_one_qstr_excl+0x126/0x2b0 fs/namei.c:1693
 do_renameat2+0x706/0x13f0 fs/namei.c:5176
 __do_sys_rename fs/namei.c:5273 [inline]
 __se_sys_rename fs/namei.c:5271 [inline]
 __x64_sys_rename+0x82/0x90 fs/namei.c:5271
 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: 0033:0x7f7cc482fad9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 17 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe074fe328 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
RAX: ffffffffffffffda RBX: 00007f7cc4878fc8 RCX: 00007f7cc482fad9
RDX: 0000000000000000 RSI: 0000000020000800 RDI: 00000000200001c0
RBP: 00007f7cc48a35f0 R08: 000055555b8934c0 R09: 000055555b8934c0
R10: 000055555b8934c0 R11: 0000000000000246 R12: 00007ffe074fe350
R13: 00007ffe074fe578 R14: 431bde82d7b634db R15: 00007f7cc487803b
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__d_unalias+0x199/0x2a0 fs/dcache.c:2969
Code: 98 00 00 00 4c 89 fb 48 c1 eb 03 49 89 ed 80 3c 2b 00 74 08 4c 89 ff e8 65 62 e7 ff 49 8b 2f 48 83 c5 68 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 48 62 e7 ff 4c 8b 5d 00 4d 85 db
RSP: 0018:ffffc90003d9fa98 EFLAGS: 00010202
RAX: 000000000000000d RBX: 1ffff1100996cb61 RCX: ffff88804d821e00
RDX: 0000000000000000 RSI: ffff88804cb65a70 RDI: ffff88804cb658f8
RBP: 0000000000000068 R08: ffff88804e530f6b R09: 1ffff11009ca61ed
R10: dffffc0000000000 R11: ffffed1009ca61ee R12: ffff88804cb65a70
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88804cb65b08
FS:  000055555b892380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe074ff000 CR3: 0000000078440000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	98                   	cwtl
   1:	00 00                	add    %al,(%rax)
   3:	00 4c 89 fb          	add    %cl,-0x5(%rcx,%rcx,4)
   7:	48 c1 eb 03          	shr    $0x3,%rbx
   b:	49 89 ed             	mov    %rbp,%r13
   e:	80 3c 2b 00          	cmpb   $0x0,(%rbx,%rbp,1)
  12:	74 08                	je     0x1c
  14:	4c 89 ff             	mov    %r15,%rdi
  17:	e8 65 62 e7 ff       	call   0xffe76281
  1c:	49 8b 2f             	mov    (%r15),%rbp
  1f:	48 83 c5 68          	add    $0x68,%rbp
  23:	48 89 e8             	mov    %rbp,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	48 89 ef             	mov    %rbp,%rdi
  34:	e8 48 62 e7 ff       	call   0xffe76281
  39:	4c 8b 5d 00          	mov    0x0(%rbp),%r11
  3d:	4d 85 db             	test   %r11,%r11


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