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* [PATCH v1] fs: Move might_sleep() annotation to iput_final()
@ 2025-11-05 19:37 Mickaël Salaün
  2025-11-05 19:50 ` Mateusz Guzik
                   ` (2 more replies)
  0 siblings, 3 replies; 8+ messages in thread
From: Mickaël Salaün @ 2025-11-05 19:37 UTC (permalink / raw)
  To: Christian Brauner
  Cc: Mickaël Salaün, linux-security-module, linux-fsdevel,
	Al Viro, Edward Adam Davis, Günther Noack, Hillf Danton,
	Jan Kara, Jann Horn, Mateusz Guzik, Max Kellermann, Tingmao Wang,
	syzbot+12479ae15958fc3f54ec

iput() don't directly call any sleepable code but mostly checks flags
and decrement a reference counter before calling iput_final() and then
evict().

Some code might call iput() with guarantees that iput_final() will not
be called.  This is the case for Landlock's hook_sb_delete() where the
inode counter must de decremented while holding it with another
reference, see comment above the first iput() call.

Move the new might_sleep() call from iput() to iput_final().  The
alternative would be to manually decrement the counter without calling
iput(), but it doesn't seem right.

Cc: Christian Brauner <brauner@kernel.org>
Cc: Edward Adam Davis <eadavis@qq.com>
Cc: Günther Noack <gnoack@google.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Max Kellermann <max.kellermann@ionos.com>
Cc: Tingmao Wang <m@maowtm.org>
Reported-by: syzbot+12479ae15958fc3f54ec@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68d32659.a70a0220.4f78.0012.GAE@google.com/
Fixes: 2ef435a872ab ("fs: add might_sleep() annotation to iput() and more")
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---

From hook_sb_delete():

	/*
	 * At this point, we own the ihold() reference that was
	 * originally set up by get_inode_object() and the
	 * __iget() reference that we just set in this loop
	 * walk.  Therefore the following call to iput() will
	 * not sleep nor drop the inode because there is now at
	 * least two references to it.
	 */
	iput(inode);

#syz test

---
 fs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 84f539497857..64120cb21e8b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1917,6 +1917,7 @@ static void iput_final(struct inode *inode)
 	const struct super_operations *op = inode->i_sb->s_op;
 	int drop;
 
+	might_sleep();
 	WARN_ON(inode_state_read(inode) & I_NEW);
 	VFS_BUG_ON_INODE(atomic_read(&inode->i_count) != 0, inode);
 
@@ -1969,7 +1970,6 @@ static void iput_final(struct inode *inode)
  */
 void iput(struct inode *inode)
 {
-	might_sleep();
 	if (unlikely(!inode))
 		return;
 
-- 
2.51.0


^ permalink raw reply related	[flat|nested] 8+ messages in thread
* [syzbot] [fs?] BUG: sleeping function called from invalid context in hook_sb_delete
@ 2025-09-23 22:59 syzbot
  2025-09-24 11:05 ` Jan Kara
  2025-10-09 20:56 ` syzbot
  0 siblings, 2 replies; 8+ messages in thread
From: syzbot @ 2025-09-23 22:59 UTC (permalink / raw)
  To: brauner, jack, linux-fsdevel, linux-kernel, syzkaller-bugs, viro

Hello,

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@syzkaller.appspotmail.com

BUG: sleeping function called from invalid context at fs/inode.c:1928
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
 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>


---
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^ permalink raw reply	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2025-11-12  5:40 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-11-05 19:37 [PATCH v1] fs: Move might_sleep() annotation to iput_final() Mickaël Salaün
2025-11-05 19:50 ` Mateusz Guzik
2025-11-05 20:56 ` [syzbot] [fs?] BUG: sleeping function called from invalid context in hook_sb_delete syzbot
2025-11-12  5:40 ` [PATCH v1] fs: Move might_sleep() annotation to iput_final() kernel test robot
  -- strict thread matches above, loose matches on Subject: below --
2025-09-23 22:59 [syzbot] [fs?] BUG: sleeping function called from invalid context in hook_sb_delete syzbot
2025-09-24 11:05 ` Jan Kara
2025-09-29  8:51   ` Christian Brauner
2025-10-09 20:56 ` syzbot

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