Re: [syzbot] [io-uring?] WARNING: ODEBUG bug in io_sq_offload_create

[Jens Axboe <axboe@kernel.dk>]

On 6/17/25 2:12 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    8c6bc74c7f89 Merge tag 'v6.16-rc1-smb3-client-fixes' of gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1745710c580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1ab5c40b21ee326a
> dashboard link: https://syzkaller.appspot.com/bug?extid=763e12bbf004fb1062e4
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13ea3d70580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10c5710c580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-8c6bc74c.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b523997774df/vmlinux-8c6bc74c.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/da5178f1b34a/bzImage-8c6bc74c.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+763e12bbf004fb1062e4@syzkaller.appspotmail.com
> 
> R13: 0000000000000002 R14: 00007fad89109ab1 R15: 00007fad8910601d
>  </TASK>
> ------------[ cut here ]------------
> ODEBUG: free active (active state 1) object: ffff888024813bd0 object type: rcu_head hint: 0x0
> WARNING: CPU: 0 PID: 5941 at lib/debugobjects.c:612 debug_print_object+0x1a2/0x2b0 lib/debugobjects.c:612
> Modules linked in:
> CPU: 0 UID: 0 PID: 5941 Comm: syz-executor101 Not tainted 6.16.0-rc1-syzkaller-00236-g8c6bc74c7f89 #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:debug_print_object+0x1a2/0x2b0 lib/debugobjects.c:612
> Code: fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 54 41 56 48 8b 14 dd 00 8a 15 8c 4c 89 e6 48 c7 c7 80 7e 15 8c e8 bf 33 99 fc 90 <0f> 0b 90 90 58 83 05 56 99 c6 0b 01 48 83 c4 18 5b 5d 41 5c 41 5d
> RSP: 0018:ffffc90003f8fa78 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: 0000000000000003 RCX: ffffffff817ae248
> RDX: ffff88803cd0a440 RSI: ffffffff817ae255 RDI: 0000000000000001
> RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000001 R12: ffffffff8c158520
> R13: ffffffff8baeb4a0 R14: 0000000000000000 R15: ffffc90003f8fb78
> FS:  00007fad890686c0(0000) GS:ffff8880d6753000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fad8911b362 CR3: 0000000031b29000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __debug_check_no_obj_freed lib/debugobjects.c:1099 [inline]
>  debug_check_no_obj_freed+0x4b7/0x600 lib/debugobjects.c:1129
>  slab_free_hook mm/slub.c:2312 [inline]
>  slab_free mm/slub.c:4643 [inline]
>  kmem_cache_free+0x2ac/0x4d0 mm/slub.c:4745
>  put_task_struct include/linux/sched/task.h:145 [inline]
>  put_task_struct include/linux/sched/task.h:132 [inline]
>  io_sq_offload_create+0xe4b/0x1330 io_uring/sqpoll.c:517
>  io_uring_create io_uring/io_uring.c:3747 [inline]
>  io_uring_setup+0x1514/0x2120 io_uring/io_uring.c:3830
>  __do_sys_io_uring_setup io_uring/io_uring.c:3864 [inline]
>  __se_sys_io_uring_setup io_uring/io_uring.c:3855 [inline]
>  __x64_sys_io_uring_setup+0xc2/0x170 io_uring/io_uring.c:3855
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fad890b6f99
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 31 1b 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 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fad89068208 EFLAGS: 00000246 ORIG_RAX: 00000000000001a9
> RAX: ffffffffffffffda RBX: 00007fad891393c8 RCX: 00007fad890b6f99
> RDX: 0000000000000000 RSI: 0000200000000200 RDI: 0000000000004d25
> RBP: 00007fad891393c0 R08: 00007fad89067fa6 R09: 0000000000003232
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fad89068210
> R13: 0000000000000002 R14: 00007fad89109ab1 R15: 00007fad8910601d
>  </TASK>

Looks like fallout from a fix in the 6.16 kernel series, where:

commit ac0b8b327a5677dc6fecdf353d808161525b1ff0
Author: Penglei Jiang <superman.xpt@gmail.com>
Date:   Tue Jun 10 10:18:01 2025 -0700

    io_uring: fix use-after-free of sq->thread in __io_uring_show_fdinfo()

moves task_struct error handling to io_sq_thread(), but misses that
io_sq_offload_create() does it too for tctx allocation failure.

#syz test: git://git.kernel.dk/linux.git syztest

-- 
Jens Axboe