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Date: Tue, 19 Jan 2016 15:05:43 +0200
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: syzkaller <syzkaller@googlegroups.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
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        Kees Cook <keescook@google.com>, Bjorn Helgaas <bhelgaas@google.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        David Drysdale <drysdale@google.com>,
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        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>
Subject: Re: [PATCH v4] kernel: add kcov code coverage
Message-ID: <20160119130543.GB20984@node.shutemov.name>
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On Tue, Jan 19, 2016 at 01:55:43PM +0100, Dmitry Vyukov wrote:
> >> +static int __init kcov_init(void)
> >> +{
> >> +     if (!debugfs_create_file("kcov", 0666, NULL, NULL, &kcov_fops)) {
> >
> > Why 0666? May be 0600?.
> 
> The idea is that it can be useful to fuzz-test under a normal user as well.
> This file is also guarded by debugfs mount permissions. Usually it is mounted
> as 0700, so normal users can't get access to it.
> However if one wants to fuzz-test under a normal user, he could mount
> debugfs as 0777 and get access to this file.
> 
> I am not very strong about this, though. If you say, I will change it to 0600.
> I open this file as root at the moment. And we can change it back
> if/when we better understand a potential use case.

I think it's safer to make it 0600. It's up to system administrator to
change permissions, if he wants give this capability to mortals.

-- 
 Kirill A. Shutemov