WARNING: ODEBUG bug in clean_demultiplex_info

Status: moderation: reported on 2026/08/21 06:57
Subsystems: cifs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+4117399679308964d5ec@syzkaller.appspotmail.com
First crash: 8d19h, last: 8d19h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
0f2689a3 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ WARNING: ODEBUG bug in clean_demultiplex_info 2026/08/19 03:09 2026/08/19 03:09 2026/08/19 03:16 1e72964b
Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 WARNING: ODEBUG bug in clean_demultiplex_info -1 1 7d14h 7d14h 0/2 upstream: reported on 2026/08/18 11:49

Sample crash report:
------------[ cut here ]------------
ODEBUG: free active (active state 0) object: ffff88807f9825d8 object type: work_struct hint: smb2_reconnect_server+0x0/0x17b0 fs/smb/client/smb2pdu.c:-1
WARNING: lib/debugobjects.c:632 at debug_print_object+0xec/0x230 lib/debugobjects.c:629, CPU#0: cifsd/6027
Modules linked in:
CPU: 0 UID: 0 PID: 6027 Comm: cifsd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:debug_print_object+0x18a/0x230 lib/debugobjects.c:629
Code: f8 48 c1 e8 03 80 3c 18 00 74 08 4c 89 ff e8 5d 0a 56 fd 4d 8b 0f 4c 89 ef 48 8b 74 24 08 48 89 ea 44 89 e1 4d 89 f0 ff 34 24 <67> 48 0f b9 3a 48 83 c4 08 ff 05 a3 2e 79 0b 48 83 c4 10 5b 41 5c
RSP: 0018:ffffc90005607700 EFLAGS: 00010246
RAX: 1ffffffff17d6ce4 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: ffffffff8c4bca40 RSI: ffffffff8c4bc4c0 RDI: ffffffff9062f4e0
RBP: ffffffff8c4bca40 R08: ffff88807f9825d8 R09: ffffffff8beb78e0
R10: dffffc0000000000 R11: ffffffff818ef8a0 R12: 0000000000000000
R13: ffffffff9062f4e0 R14: ffff88807f9825d8 R15: ffffffff8beb6720
FS:  0000000000000000(0000) GS:ffff888124f49000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b3320cff8 CR3: 0000000059ce9000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 __debug_check_no_obj_freed lib/debugobjects.c:1171 [inline]
 debug_check_no_obj_freed+0x2e3/0x450 lib/debugobjects.c:1201
 slab_free_hook mm/slub.c:2608 [inline]
 slab_free mm/slub.c:6377 [inline]
 kfree+0x13e/0x640 mm/slub.c:6692
 clean_demultiplex_info+0xb24/0xd30 fs/smb/client/connect.c:1146
 cifs_demultiplex_thread+0x2fb9/0x3310 fs/smb/client/connect.c:1439
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
----------------
Code disassembly (best guess):
   0:	f8                   	clc
   1:	48 c1 e8 03          	shr    $0x3,%rax
   5:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1)
   9:	74 08                	je     0x13
   b:	4c 89 ff             	mov    %r15,%rdi
   e:	e8 5d 0a 56 fd       	call   0xfd560a70
  13:	4d 8b 0f             	mov    (%r15),%r9
  16:	4c 89 ef             	mov    %r13,%rdi
  19:	48 8b 74 24 08       	mov    0x8(%rsp),%rsi
  1e:	48 89 ea             	mov    %rbp,%rdx
  21:	44 89 e1             	mov    %r12d,%ecx
  24:	4d 89 f0             	mov    %r14,%r8
  27:	ff 34 24             	push   (%rsp)
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	48 83 c4 08          	add    $0x8,%rsp
  33:	ff 05 a3 2e 79 0b    	incl   0xb792ea3(%rip)        # 0xb792edc
  39:	48 83 c4 10          	add    $0x10,%rsp
  3d:	5b                   	pop    %rbx
  3e:	41 5c                	pop    %r12

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/17 06:45 upstream dcb68831eac7 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root WARNING: ODEBUG bug in clean_demultiplex_info
* Struck through repros no longer work on HEAD.