linux-kernel - Re: [PATCH 2/2] tracefs: Only clobber mode/uid/gid on remount if asked

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Message-ID: <20220907212542.513afad2@gandalf.local.home>
Date:   Wed, 7 Sep 2022 21:25:42 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] tracefs: Only clobber mode/uid/gid on remount if
 asked

On Wed, 7 Sep 2022 13:52:15 -0700
Brian Norris <briannorris@...omium.org> wrote:

> Existing behavior:
> 
>   ## Pre-existing status: tracefs is 0755.
>   # stat -c '%A' /sys/kernel/tracing/
>   drwxr-xr-x
> 
>   ## (Re)trigger the automount.
>   # umount /sys/kernel/debug/tracing
>   # stat -c '%A' /sys/kernel/debug/tracing/.
>   drwx------
> 
>   ## Unexpected: the automount changed mode for other mount instances.
>   # stat -c '%A' /sys/kernel/tracing/
>   drwx------
> 
> New behavior:
> 
>   ## Pre-existing status: tracefs is 0755.
>   # stat -c '%A' /sys/kernel/tracing/
>   drwxr-xr-x
> 
>   ## (Re)trigger the automount.
>   # umount /sys/kernel/debug/tracing
>   # stat -c '%A' /sys/kernel/debug/tracing/.
>   drwxr-xr-x
> 
>   ## Expected: the automount does not change other mount instances.
>   # stat -c '%A' /sys/kernel/tracing/
>   drwxr-xr-x

Thanks!

Here's the new change log:

-- Steve

From: Brian Norris <briannorris@...omium.org>
Subject: [PATCH] tracefs: Only clobber mode/uid/gid on remount if asked

Users may have explicitly configured their tracefs permissions; we
shouldn't overwrite those just because a second mount appeared.

Only clobber if the options were provided at mount time.

Note: the previous behavior was especially surprising in the presence of
automounted /sys/kernel/debug/tracing/.

Existing behavior:

  ## Pre-existing status: tracefs is 0755.
  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

  ## (Re)trigger the automount.
  # umount /sys/kernel/debug/tracing
  # stat -c '%A' /sys/kernel/debug/tracing/.
  drwx------

  ## Unexpected: the automount changed mode for other mount instances.
  # stat -c '%A' /sys/kernel/tracing/
  drwx------

New behavior (after this change):

  ## Pre-existing status: tracefs is 0755.
  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

  ## (Re)trigger the automount.
  # umount /sys/kernel/debug/tracing
  # stat -c '%A' /sys/kernel/debug/tracing/.
  drwxr-xr-x

  ## Expected: the automount does not change other mount instances.
  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x


Signed-off-by: Brian Norris <briannorris@...omium.org>