linux-kernel - Re: [BUG] landlock: sleeping function called from invalid context in hook_sb

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Message-ID: <20251120.c5c17c664315@gnoack.org>
Date: Thu, 20 Nov 2025 09:48:43 +0100
From: Günther Noack <gnoack3000@...il.com>
To: 许佳凯 <xujiakai24@...ls.ucas.ac.cn>
Cc: linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
	Günther Noack <gnoack@...gle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Mickaël Salaün <mic@...ikod.net>
Subject: Re: [BUG] landlock: sleeping function called from invalid context in
 hook_sb_delete()

Hello!

Thanks for the report!

CC-ing Mickaël, who authored that code

On Wed, Nov 12, 2025 at 10:35:17AM +0800, 许佳凯 wrote:
> The call trace indicates that hook_sb_delete() holds s_inode_list_lock (a spinlock) while invoking operations that may eventually call iput(), which can sleep.
> This violates the locking context expectations and triggers __might_sleep() warnings.
> The issue seems to be related to how Landlock handles superblock cleanup during security_sb_delete().
> 
> 
> I’m currently only reporting this issue to the community; the exact fix will likely need to be confirmed and implemented by the Landlock and filesystem maintainers.

This looks like a false positive to me.

There are three places where iput() is being called in hook_sb_delete,
two of them are in places where it is *not* holding the
s_inode_list_lock.  The one that *is* holding the s_inode_list_lock
has the following comment:

/*
 * 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.
 */

That seems to indicate that the sleepability concern was taken into
consideration.  iput() only sleeps if the refcount reaches zero, and
if you can exclude that, it won't sleep.

—Günther

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