linux-kernel - Re: NULL pointer dereference regression when running `chmod -R root:tracing /sys/kernel/debug/tracing`

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Date:   Tue, 14 Nov 2023 08:55:29 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Linux regression tracking #adding (Thorsten Leemhuis)" 
        <regressions@...mhuis.info>
Cc:     Linux regressions mailing list <regressions@...ts.linux.dev>,
        Milian Wolff <milian.wolff@...b.com>, akaher@...are.com,
        akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        mhiramat@...nel.org
Subject: Re: NULL pointer dereference regression when running `chmod -R
 root:tracing /sys/kernel/debug/tracing`

On Tue, 14 Nov 2023 14:38:57 +0100
"Linux regression tracking #adding (Thorsten Leemhuis)" <regressions@...mhuis.info> wrote:

> [TLDR: I'm adding this report to the list of tracked Linux kernel
> regressions; the text you find below is based on a few templates
> paragraphs you might have encountered already in similar form.
> See link in footer if these mails annoy you.]
> 
> On 12.11.23 11:41, Milian Wolff wrote:
> > 
> > this patch seems to have introduced a kernel bug causing
> > a NULL pointer dereference when one runs:
> > 
> >     sudo chown -R root:tracing /sys/kernel/debug/tracing/
> > 
> > See the archlinux bug report I created initially for some more information:
> > https://bugs.archlinux.org/task/80230
> > 
> > With 6.6.1 and 9aaee3eebc91dd9ccebf6b6bc8a5f59d04ef718b reverted,
> > the above `chmod` command works. With a normal 6.6.1 build, or re-applying
> > the patch again, the command fails and `dmesg` shows:  
> 
> Steven is already working on this, but to ensure the issue doesn't fall
> through the cracks unnoticed, I'm adding it to regzbot, the Linux kernel
> regression tracking bot (and from the context I assume it happens in
> mainline as well)

Note, the code in question was rewritten in 6.7 and the bug does not
exist there. It only exists in 6.6 and I already sent Greg the patch,
and he told me that it's in his queue.

It's only a regression in 6.6 and not in mainline.

-- Steve