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 16:06:38 +0100
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Steven Rostedt <rostedt@...dmis.org>
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 14.11.23 14:55, Steven Rostedt wrote:
> 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.

Ahh, sorry fot getting this wrong and thx for letting me know.

#regzbot introduced 9aaee3eebc91dd9ccebf6b6bc8a5f59d04ef718b
#regzbot fix: eventfs: Check for NULL ef in eventfs_set_attr()

Ciao, Thorsten

P.S.: Enjoy LPC, hope to be there again next year.