linux-kernel - Re: [PATCH 1/3] module: Invalidate signatures on force-loaded modules

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Message-ID: <1461704447.5852.17.camel@decadent.org.uk>
Date:	Tue, 26 Apr 2016 23:00:47 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	David Howells <dhowells@...hat.com>,
	David Woodhouse <dwmw2@...radead.org>,
	keyrings@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] module: Invalidate signatures on force-loaded
 modules

On Tue, 2016-04-26 at 20:07 +0930, Rusty Russell wrote:
> Ben Hutchings <ben@...adent.org.uk> writes:
> > 
> > Signing a module should only make it trusted by the specific kernel it
> > was built for, not anything else.  Loading a signed module meant for a
> > kernel with a different ABI could have interesting effects.
> > Therefore, treat all signatures as invalid when a module is
> > force-loaded.
> > 
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > Cc: stable@...r.kernel.org
> > ---
> >  kernel/module.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 66426f743c29..649b1827ed15 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -2599,13 +2599,18 @@ static inline void kmemleak_load_module(const struct module *mod,
> >  #endif
> >  
> >  #ifdef CONFIG_MODULE_SIG
> > -static int module_sig_check(struct load_info *info)
> > +static int module_sig_check(struct load_info *info, int flags)
> >  {
> >  	int err = -ENOKEY;
> >  	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
> >  	const void *mod = info->hdr;
> >  
> > -	if (info->len > markerlen &&
> > +	/*
> > +	 * Require flags == 0, as a module with version information
> > +	 * removed is no longer the module that was signed
> > +	 */
> > +	if (flags == 0 &&
> This check is a bit lazy.  We could have other flags in future,
> so this should really be !(flags &
> (MODULE_INIT_IGNORE_MODVERSIONS|MODULE_INIT_IGNORE_VERMAGIC) right?

Yes we could, but I'd prefer this to fail-safe in case no-one thinks
about whether it should be updated then.

Ben.

-- 
Ben Hutchings
The generation of random numbers is too important to be left to chance.
                                                            - Robert Coveyou
Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)