linux-kernel - Re: [PATCH] debugfs: fix mount options not being applied

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Message-ID: <a1b3f555-acfe-4fd1-8aa4-b97f456fd6f4@redhat.com>
Date: Mon, 4 Aug 2025 12:22:23 -0500
From: Eric Sandeen <sandeen@...hat.com>
To: Charalampos Mitrodimas <charmitro@...teo.net>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>,
 Christian Brauner <brauner@...nel.org>, David Howells <dhowells@...hat.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] debugfs: fix mount options not being applied

On 8/4/25 9:30 AM, Charalampos Mitrodimas wrote:
> Mount options (uid, gid, mode) are silently ignored when debugfs is
> mounted. This is a regression introduced during the conversion to the
> new mount API.
> 
> When the mount API conversion was done, the line that sets
> sb->s_fs_info to the parsed options was removed. This causes
> debugfs_apply_options() to operate on a NULL pointer.
> 
> As an example, with the bug the "mode" mount option is ignored:
> 
>   $ mount -o mode=0666 -t debugfs debugfs /tmp/debugfs_test
>   $ mount | grep debugfs_test
>   debugfs on /tmp/debugfs_test type debugfs (rw,relatime)
>   $ ls -ld /tmp/debugfs_test
>   drwx------ 25 root root 0 Aug  4 14:16 /tmp/debugfs_test

Argh. So, this looks a lot like the issue that got fixed for tracefs in:

e4d32142d1de tracing: Fix tracefs mount options

Let me look at this; tracefs & debugfs are quite similar, so perhaps
keeping the fix consistent would make sense as well but I'll dig
into it a bit more.

Thanks,
-Eric