Re: [PATCH v2] kernel: add panic_on_taint

From: Luis Chamberlain <mcgrof@kernel.org>
To: Rafael Aquini <aquini@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org,
	dyoung@redhat.com, bhe@redhat.com, corbet@lwn.net,
	keescook@chromium.org, akpm@linux-foundation.org, cai@lca.pw,
	rdunlap@infradead.org
Subject: Re: [PATCH v2] kernel: add panic_on_taint
Date: Thu, 7 May 2020 18:22:57 +0000	[thread overview]
Message-ID: <20200507182257.GX11244@42.do-not-panic.com> (raw)
In-Reply-To: <20200507180631.308441-1-aquini@redhat.com>

On Thu, May 07, 2020 at 02:06:31PM -0400, Rafael Aquini wrote:
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 8a176d8727a3..b80ab660d727 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1217,6 +1217,13 @@ static struct ctl_table kern_table[] = {
>  		.extra1		= SYSCTL_ZERO,
>  		.extra2		= SYSCTL_ONE,
>  	},
> +	{
> +		.procname	= "panic_on_taint",
> +		.data		= &panic_on_taint,
> +		.maxlen		= sizeof(unsigned long),
> +		.mode		= 0644,
> +		.proc_handler	= proc_doulongvec_minmax,
> +	},

You sent this out before I could reply to the other thread on v1.
My thoughts on the min / max values, or lack here:

Valid range doesn't mean "currently allowed defined" masks.                     

For example, if you expect to panic due to a taint, but a new taint type
you want was not added on an older kernel you would be under a very
*false* sense of security that your kernel may not have hit such a
taint, but the reality of the situation was that the kernel didn't
support that taint flag only added in future kernels.                           

You may need to define a new flag (MAX_TAINT) which should be the last
value + 1, the allowed max values would be                                      

(2^MAX_TAINT)-1                                                                 

or                                                                              

(1<<MAX_TAINT)-1  

Since this is to *PANIC* I think we do want to test ranges and ensure
only valid ones are allowed.

  Luis