linux-kernel - Re: [PATCH v4] kernel: add kcov code coverage

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Message-ID: <CACT4Y+Z9OSwhV3CMhKg+b0wrwvh6f8f-Kgj_xumjKAtkL=YcBA@mail.gmail.com>
Date:	Tue, 19 Jan 2016 15:02:17 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	syzkaller <syzkaller@...glegroups.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Tavis Ormandy <taviso@...gle.com>,
	Will Deacon <will.deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Kees Cook <keescook@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Drysdale <drysdale@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
Subject: Re: [PATCH v4] kernel: add kcov code coverage

On Tue, Jan 19, 2016 at 2:05 PM, Kirill A. Shutemov
<kirill@...temov.name> wrote:
> 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.

Great! I've missed the possibility of chmoding it afterwards. Will
change to 0600 in next version.