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

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Message-ID: <20200509034854.GI11244@42.do-not-panic.com>
Date:   Sat, 9 May 2020 03:48:54 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Rafael Aquini <aquini@...hat.com>
Cc:     Tso Ted <tytso@....edu>, Adrian Bunk <bunk@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Laura Abbott <labbott@...hat.com>,
        Jeff Mahoney <jeffm@...e.com>, Jiri Kosina <jikos@...nel.org>,
        Jessica Yu <jeyu@...e.de>, Takashi Iwai <tiwai@...e.de>,
        Ann Davis <AnDavis@...e.com>,
        Richard Palethorpe <rpalethorpe@...e.de>,
        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 Fri, May 08, 2020 at 08:47:19AM -0400, Rafael Aquini wrote:
> On Thu, May 07, 2020 at 10:25:58PM +0000, Luis Chamberlain wrote:
> > On Thu, May 07, 2020 at 06:06:06PM -0400, Rafael Aquini wrote:
> > > On Thu, May 07, 2020 at 08:33:40PM +0000, Luis Chamberlain wrote:
> > > > I *think* that a cmdline route to enable this would likely remove the
> > > > need for the kernel config for this. But even with Vlastimil's work
> > > > merged, I think we'd want yet-another value to enable / disable this
> > > > feature. Do we need yet-another-taint flag to tell us that this feature
> > > > was enabled?
> > > >
> > > 
> > > I guess it makes sense to get rid of the sysctl interface for
> > > proc_on_taint, and only keep it as a cmdline option. 
> > 
> > That would be easier to support and k3eps this simple.
> > 
> > > But the real issue seems to be, regardless we go with a cmdline-only option
> > > or not, the ability of proc_taint() to set any arbitrary taint flag 
> > > other than just marking the kernel with TAINT_USER. 
> > 
> > I think we would have no other option but to add a new TAINT flag so
> > that we know that the taint flag was modified by a user. Perhaps just
> > re-using TAINT_USER when proc_taint() would suffice.
> >
> 
> We might not need an extra taint flag if, perhaps, we could make these
> two features mutually exclusive. The idea here is that bitmasks added 
> via panic_on_taint get filtered out in proc_taint(), so a malicious 
> user couldn't exploit the latter interface to easily panic the system,
> when the first one is also in use. 

I get it, however I I can still see the person who enables enabling
panic-on-tain wanting to know if proc_taint() was used. So even if
it was not on their mask, if it was modified that seems like important
information for a bug report analysis.

  Luis