linux-kernel - Re: [PATCH v2] kernel: add panic_on

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Date:   Thu, 7 May 2020 14:47:05 -0400
From:   Rafael Aquini <aquini@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        dyoung@...hat.com, bhe@...hat.com, corbet@....net,
        keescook@...omium.org, akpm@...ux-foundation.org, cai@....pw,
        rdunlap@...radead.org
Subject: Re: [PATCH v2] kernel: add panic_on_taint

On Thu, May 07, 2020 at 02:43:16PM -0400, Rafael Aquini wrote:
> On Thu, May 07, 2020 at 06:22:57PM +0000, Luis Chamberlain wrote:
> > 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.
> >
> 
> Ok. I'm thinking in:
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 8a176d8727a3..ee492431e7b0 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1217,6 +1217,15 @@ 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,
> +               .extra1         = SYSCTL_ZERO,
> +               .extra2         = (1 << TAINT_FLAGS_COUNT << 1) - 1,
							^^^^^^^^
Without that crap, obviously. Sorry. That was a screw up on my side,
when copyin' and pasting.

-- Rafael
	
> +       },
> 
> 
> Would that address your concerns wrt this one?
> 
> Cheers!
> -- Rafael