Received-SPF: pass (google.com: domain of linux-kernel+bounces-162967-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Date: Mon, 29 Apr 2024 12:49:04 -0700
From: Kees Cook <keescook@chromium.org>
To: Allen Pais <apais@linux.microsoft.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, viro@zeniv.linux.org.uk, brauner@kernel.org,
	jack@suse.cz, ebiederm@xmission.com, mcgrof@kernel.org,
	j.granados@samsung.com
Subject: Re: [RFC PATCH] fs/coredump: Enable dynamic configuration of max
 file note size
Message-ID: <202404291245.18281A6D@keescook>
References: <20240429172128.4246-1-apais@linux.microsoft.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240429172128.4246-1-apais@linux.microsoft.com>

On Mon, Apr 29, 2024 at 05:21:28PM +0000, Allen Pais wrote:
> Introduce the capability to dynamically configure the maximum file
> note size for ELF core dumps via sysctl. This enhancement removes
> the previous static limit of 4MB, allowing system administrators to
> adjust the size based on system-specific requirements or constraints.

Under what conditions is this actually needed?

> [...]
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 81cc974913bb..80cdc37f2fa2 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -63,6 +63,7 @@
>  #include <linux/mount.h>
>  #include <linux/userfaultfd_k.h>
>  #include <linux/pid.h>
> +#include <linux/coredump.h>
>  
>  #include "../lib/kstrtox.h"
>  
> @@ -1623,6 +1624,13 @@ static struct ctl_table kern_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec,
>  	},
> +	{
> +		.procname       = "max_file_note_size",
> +		.data           = &max_file_note_size,
> +		.maxlen         = sizeof(unsigned int),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec,
> +	},

Please don't add new sysctls to kernel/sysctl.c. Put this in fs/coredump.c
instead, and name it "core_file_note_size_max". (A "max" suffix is more
common than prefixes, and I'd like it clarified that it relates to the
coredumper with the "core" prefix that match the other coredump sysctls.

-Kees

-- 
Kees Cook