syzbot


general protection fault in nilfs_mdt_save_to_shadow_map

Status: upstream: reported C repro on 2026/04/16 08:31
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+78987da922319afcebc1@syzkaller.appspotmail.com
First crash: 3d09h, last: 6h53m
Bug presence (2)
Date Name Commit Repro Result
2026/04/17 linux-6.6.y (ToT) 8cee53b8eaeb C [report] general protection fault in nilfs_mdt_save_to_shadow_map
2026/04/17 upstream (ToT) 43cfbdda5af6 C Didn't crash
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 general protection fault in nilfs_mdt_save_to_shadow_map origin:upstream 2 C 12 7h02m 16d 0/3 upstream: reported C repro on 2026/04/03 15:20
upstream general protection fault in nilfs_mdt_save_to_shadow_map nilfs 2 C error 87 5d11h 33d 25/29 upstream: reported C repro on 2026/03/17 03:14
linux-6.1 BUG: unable to handle kernel paging request in nilfs_mdt_save_to_shadow_map 8 C 15 6h43m 31d 0/3 upstream: reported C repro on 2026/03/19 02:00
Fix bisection attempts (1)
Created Duration User Patch Repo Result
2026/04/18 13:12 33m fix candidate upstream error job log

Sample crash report:
syz.0.17[5917]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
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
general protection fault, probably for non-canonical address 0xdffffc0000000008: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000040-0x0000000000000047]
CPU: 1 PID: 5917 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:nilfs_mdt_save_to_shadow_map+0x141/0x1c0 fs/nilfs2/mdt.c:549
Code: 3f 4c 8d 63 d8 4c 89 e0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 e7 e8 4e 11 9a fe 4d 8b 24 24 49 83 c4 40 4c 89 e0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 e7 e8 30 11 9a fe 49 8b 34 24 4c 89 ff
RSP: 0018:ffffc90003247808 EFLAGS: 00010202
RAX: 0000000000000008 RBX: ffff8880631f0158 RCX: 0000000000000000
RDX: ffff8880268cda00 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff8e8b14ef R09: 1ffffffff1d1629d
R10: dffffc0000000000 R11: fffffbfff1d1629e R12: 0000000000000040
R13: dffffc0000000000 R14: ffff88801cfd4d40 R15: ffff8880631f1050
FS:  000055557b18a500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33f63fff CR3: 0000000075a5e000 CR4: 00000000003506e0
Call Trace:
 <TASK>
 nilfs_clean_segments+0x163/0xa40 fs/nilfs2/segment.c:2513
 nilfs_ioctl_clean_segments fs/nilfs2/ioctl.c:940 [inline]
 nilfs_ioctl+0x203f/0x21a0 fs/nilfs2/ioctl.c:1304
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fd8a179c819
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:00007ffdf5639008 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd8a1a15fa0 RCX: 00007fd8a179c819
RDX: 0000200000000640 RSI: 0000000040786e88 RDI: 0000000000000004
RBP: 00007fd8a1832c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd8a1a15fac R14: 00007fd8a1a15fa0 R15: 00007fd8a1a15fa0
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:nilfs_mdt_save_to_shadow_map+0x141/0x1c0 fs/nilfs2/mdt.c:549
Code: 3f 4c 8d 63 d8 4c 89 e0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 e7 e8 4e 11 9a fe 4d 8b 24 24 49 83 c4 40 4c 89 e0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 e7 e8 30 11 9a fe 49 8b 34 24 4c 89 ff
RSP: 0018:ffffc90003247808 EFLAGS: 00010202
RAX: 0000000000000008 RBX: ffff8880631f0158 RCX: 0000000000000000
RDX: ffff8880268cda00 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff8e8b14ef R09: 1ffffffff1d1629d
R10: dffffc0000000000 R11: fffffbfff1d1629e R12: 0000000000000040
R13: dffffc0000000000 R14: ffff88801cfd4d40 R15: ffff8880631f1050
FS:  000055557b18a500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33f63fff CR3: 0000000075a5e000 CR4: 00000000003506e0
----------------
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 4e 11 9a fe       	call   0xfe9a1168
  1a:	4d 8b 24 24          	mov    (%r12),%r12
  1e:	49 83 c4 40          	add    $0x40,%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 30 11 9a fe       	call   0xfe9a1168
  38:	49 8b 34 24          	mov    (%r12),%rsi
  3c:	4c 89 ff             	mov    %r15,%rdi

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/17 12:32 linux-6.6.y 8cee53b8eaeb de0a551d .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-6-6-kasan general protection fault in nilfs_mdt_save_to_shadow_map
2026/04/17 12:04 linux-6.6.y 8cee53b8eaeb de0a551d .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-6-6-kasan general protection fault in nilfs_mdt_save_to_shadow_map
2026/04/19 11:26 linux-6.6.y 9760bf04666d 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan general protection fault in nilfs_mdt_save_to_shadow_map
2026/04/19 11:25 linux-6.6.y 9760bf04666d 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan general protection fault in nilfs_mdt_save_to_shadow_map
2026/04/16 08:30 linux-6.6.y 8cee53b8eaeb df15c5f3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan general protection fault in nilfs_mdt_save_to_shadow_map
2026/04/16 08:30 linux-6.6.y 8cee53b8eaeb df15c5f3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan general protection fault in nilfs_mdt_save_to_shadow_map
* Struck through repros no longer work on HEAD.