Re: [syzbot] [nilfs?] general protection fault in nilfs_mdt_save_to_shadow_map

[syzbot <syzbot+4b4093b1f24ad789bf37@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in nilfs_mdt_save_to_shadow_map

loop0: detected capacity change from 0 to 4096
NILFS (loop0): invalid segment: Checksum error in segment payload
NILFS (loop0): trying rollback from an earlier position
NILFS (loop0): recovery complete
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
CPU: 1 UID: 0 PID: 6533 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:nilfs_mdt_save_to_shadow_map+0x141/0x1c0 fs/nilfs2/mdt.c:559
Code: 3f 4c 8d 63 d8 4c 89 e0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 e7 e8 de c8 82 fe 4d 8b 24 24 49 83 c4 30 4c 89 e0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 e7 e8 c0 c8 82 fe 49 8b 34 24 4c 89 ff
RSP: 0018:ffffc90003467708 EFLAGS: 00010206
RAX: 0000000000000006 RBX: ffff888058b3c560 RCX: 0000000000000000
RDX: ffff888031629e80 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffff888031629e80 R09: 0000000000000003
R10: 0000000000000406 R11: 0000000000000000 R12: 0000000000000030
R13: dffffc0000000000 R14: ffff88801cadd138 R15: ffff888058b3bb18
FS:  00007f88139416c0(0000) GS:ffff888125537000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2e963fff CR3: 0000000023756000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 nilfs_clean_segments+0x162/0xa50 fs/nilfs2/segment.c:2521
 nilfs_ioctl_clean_segments fs/nilfs2/ioctl.c:916 [inline]
 nilfs_ioctl+0x261f/0x2780 fs/nilfs2/ioctl.c:1346
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f881299c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8813941028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f8812c15fa0 RCX: 00007f881299c799
RDX: 0000200000000640 RSI: 0000000040786e88 RDI: 0000000000000004
RBP: 00007f8812a32c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8812c16038 R14: 00007f8812c15fa0 R15: 00007fff51656638
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:nilfs_mdt_save_to_shadow_map+0x141/0x1c0 fs/nilfs2/mdt.c:559
Code: 3f 4c 8d 63 d8 4c 89 e0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 e7 e8 de c8 82 fe 4d 8b 24 24 49 83 c4 30 4c 89 e0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 e7 e8 c0 c8 82 fe 49 8b 34 24 4c 89 ff
RSP: 0018:ffffc90003467708 EFLAGS: 00010206
RAX: 0000000000000006 RBX: ffff888058b3c560 RCX: 0000000000000000
RDX: ffff888031629e80 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffff888031629e80 R09: 0000000000000003
R10: 0000000000000406 R11: 0000000000000000 R12: 0000000000000030
R13: dffffc0000000000 R14: ffff88801cadd138 R15: ffff888058b3bb18
FS:  00007f88139416c0(0000) GS:ffff888125437000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f88129e9e80 CR3: 0000000023756000 CR4: 00000000003526f0
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	4c 8d 63 d8          	lea    -0x28(%rbx),%r12
   4:	4c 89 e0             	mov    %r12,%rax
   7:	48 c1 e8 03          	shr    $0x3,%rax
   b:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
  10:	74 08                	je     0x1a
  12:	4c 89 e7             	mov    %r12,%rdi
  15:	e8 de c8 82 fe       	call   0xfe82c8f8
  1a:	4d 8b 24 24          	mov    (%r12),%r12
  1e:	49 83 c4 30          	add    $0x30,%r12
  22:	4c 89 e0             	mov    %r12,%rax
  25:	48 c1 e8 03          	shr    $0x3,%rax
* 29:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2e:	74 08                	je     0x38
  30:	4c 89 e7             	mov    %r12,%rdi
  33:	e8 c0 c8 82 fe       	call   0xfe82c8f8
  38:	49 8b 34 24          	mov    (%r12),%rsi
  3c:	4c 89 ff             	mov    %r15,%rdi


Tested on:

commit:         95c541dd Add linux-next specific files for 20260316
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12f93d52580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ed431987028345c6
dashboard link: https://syzkaller.appspot.com/bug?extid=4b4093b1f24ad789bf37
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1650a8da580000