Message-ID: <fnxbqe3nlcptxqcs7tkt6qnacupkxu2xn4duwc6g6n2bk4tstb@hi2gl5cwishr>
Date: Wed, 24 Sep 2025 13:05:03 +0200
From: Jan Kara <jack@...e.cz>
To: syzbot <syzbot+12479ae15958fc3f54ec@...kaller.appspotmail.com>
Cc: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk, 
	Mickaël Salaün <mic@...ikod.net>, linux-security-module@...r.kernel.org, 
	Günther Noack <gnoack@...gle.com>
Subject: Re: [syzbot] [fs?] BUG: sleeping function called from invalid
 context in hook_sb_delete

Hello!

Added Landlock guys to CC since this is a bug in Landlock.

On Tue 23-09-25 15:59:37, syzbot wrote:
> syzbot found the following issue on:
> 
> HEAD commit:    ce7f1a983b07 Add linux-next specific files for 20250923
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=118724e2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1be6fa3d47bce66e
> dashboard link: https://syzkaller.appspot.com/bug?extid=12479ae15958fc3f54ec
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1376e27c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=136e78e2580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/c30be6f36c31/disk-ce7f1a98.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ae9ea347d4d8/vmlinux-ce7f1a98.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d59682a4f33c/bzImage-ce7f1a98.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+12479ae15958fc3f54ec@...kaller.appspotmail.com
> 
> BUG: sleeping function called from invalid context at fs/inode.c:1928

The first catch from the new might_sleep() annotations in iput().

> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 6028, name: syz.0.17
> preempt_count: 1, expected: 0
> RCU nest depth: 0, expected: 0
> 2 locks held by syz.0.17/6028:
>  #0: ffff8880326bc0e0 (&type->s_umount_key#48){+.+.}-{4:4}, at: __super_lock fs/super.c:57 [inline]
>  #0: ffff8880326bc0e0 (&type->s_umount_key#48){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:72 [inline]
>  #0: ffff8880326bc0e0 (&type->s_umount_key#48){+.+.}-{4:4}, at: deactivate_super+0xa9/0xe0 fs/super.c:505
>  #1: ffff8880326bc998 (&s->s_inode_list_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
>  #1: ffff8880326bc998 (&s->s_inode_list_lock){+.+.}-{3:3}, at: hook_sb_delete+0xae/0xbd0 security/landlock/fs.c:1405
> Preemption disabled at:
> [<0000000000000000>] 0x0
> CPU: 0 UID: 0 PID: 6028 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  __might_resched+0x495/0x610 kernel/sched/core.c:8960
>  iput+0x2b/0xc50 fs/inode.c:1928
>  hook_sb_delete+0x6b5/0xbd0 security/landlock/fs.c:1468

Indeed looks like a bug because we can call iput() while holding
sb->s_inode_list_lock in one case in hook_sb_delete().

								Honza

>  security_sb_delete+0x80/0x150 security/security.c:1467
>  generic_shutdown_super+0xaa/0x2c0 fs/super.c:634
>  kill_anon_super fs/super.c:1281 [inline]
>  kill_litter_super+0x76/0xb0 fs/super.c:1291
>  deactivate_locked_super+0xbc/0x130 fs/super.c:473
>  cleanup_mnt+0x425/0x4c0 fs/namespace.c:1327
>  task_work_run+0x1d4/0x260 kernel/task_work.c:227
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop+0xe9/0x130 kernel/entry/common.c:43
>  exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
>  syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
>  syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
>  do_syscall_64+0x2bd/0xfa0 arch/x86/entry/syscall_64.c:100
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fc08e18eec9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffcd5efff18 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
> RAX: 0000000000000000 RBX: 00007fc08e3e5fa0 RCX: 00007fc08e18eec9
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00002000000002c0
> RBP: 00007fc08e211f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fc08e3e5fa0 R14: 00007fc08e3e5fa0 R15: 0000000000000002
>  </TASK>
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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