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Date:   Thu, 7 May 2020 14:43:07 -0400
From:   Rafael Aquini <aquini@redhat.com>
To:     Luis Chamberlain <mcgrof@kernel.org>
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
Message-ID: <20200507184307.GF205881@optiplex-lnx>
References: <20200507180631.308441-1-aquini@redhat.com>
 <20200507182257.GX11244@42.do-not-panic.com>
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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,
+       },


Would that address your concerns wrt this one?

Cheers!
-- Rafael