linux-kernel - RE: [RESEND v5 2/4] fs: debugfs: Add write functionality to debugfs blobs

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Message-ID: <SJ1PR11MB6083BC35F108E319B7C898DAFCB0A@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Thu, 16 Nov 2023 18:44:33 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Avadhut Naik <avadnaik@....com>
CC:     "rafael@...nel.org" <rafael@...nel.org>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "james.morse@....com" <james.morse@....com>,
        "bp@...en8.de" <bp@...en8.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexey.kardashevskiy@....com" <alexey.kardashevskiy@....com>,
        "yazen.ghannam@....com" <yazen.ghannam@....com>,
        Avadhut Naik <avadhut.naik@....com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: RE: [RESEND v5 2/4] fs: debugfs: Add write functionality to debugfs
 blobs

> > The minimalist change here would be to s/0444/0666/
> >
> Just realized that s/0444/0644/ might be an even more minimalist change since you anyways,
> I think, need to be root for error injection through einj. Does that sound good?

You need write access. I don't think you need to be root. E.g. a validation system might
set up an "einj" group and "chmod" all these files to 0664. But that's nitpicking.

>
> In any case, using 0666 will result in the below checkpatch warning:
>
> [root avadnaik-linux]# ./scripts/checkpatch.pl --strict -g HEAD
> WARNING: Exporting world writable files is usually an error. Consider more restrictive permissions.
> #84: FILE: fs/debugfs/file.c:1063:
> +       return debugfs_create_file_unsafe(name, mode & 0666, parent, blob, &fops_blob);
>
> total: 0 errors, 1 warnings, 0 checks, 54 lines checked

The warning is dubious. This code isn't necessarily exporting a world writeable file. But
it does allow a caller of this routine to do that.

>
> Would you be okay with s/0444/0644/?

> -       return debugfs_create_file_unsafe(name, mode & 0444, parent, blob, &fops_blob);
> +       return debugfs_create_file_unsafe(name, mode & 0644, parent, blob, &fops_blob);


Yes. This is fine (better). Make sure to mention in the commit comment that this allows
callers to create files writeable by owner.

-Tony