linux-kernel - Re: [PATCH] coredump: Do not lock during 'comm' reporting

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Message-ID: <202409281449.B228D0C1E7@keescook>
Date: Sat, 28 Sep 2024 14:51:06 -0700
From: Kees Cook <kees@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Vegard Nossum <vegard.nossum@...cle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Allen Pais <apais@...ux.microsoft.com>,
	Roman Kisel <romank@...ux.microsoft.com>,
	Xiaoming Ni <nixiaoming@...wei.com>,
	Vijay Nag <nagvijay@...rosoft.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] coredump: Do not lock during 'comm' reporting

On Sat, Sep 28, 2024 at 02:46:36PM -0700, Andrew Morton wrote:
> On Sat, 28 Sep 2024 14:39:45 -0700 Kees Cook <kees@...nel.org> wrote:
> 
> > On Sat, Sep 28, 2024 at 02:35:32PM -0700, Andrew Morton wrote:
> > > On Sat, 28 Sep 2024 14:08:31 -0700 Kees Cook <kees@...nel.org> wrote:
> > > 
> > > > The 'comm' member will always be NUL terminated,
> > > 
> > > Why is this?  I thought this is only true if the caller holds task_lock()?
> > 
> > Because it's always written with strscpy_pad(). The final byte will
> > always be NUL. (And this has been true for a very long time.)
> 
> So why does __get_task_comm() need to take task_lock()?

That was to make sure we didn't end up with garbled results, but
discussions have determined that we don't care:
https://lore.kernel.org/all/20240828030321.20688-1-laoar.shao@gmail.com/

But just for safety's sake, I'll change this memcpy to:

    memcpy_and_pad(comm, sizeof(comm), current->comm, sizeof(comm) - 1, 0);

-- 
Kees Cook