Message-ID: <1461704447.5852.17.camel@decadent.org.uk>
Subject: Re: [PATCH 1/3] module: Invalidate signatures on force-loaded
 modules
From: Ben Hutchings <ben@decadent.org.uk>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: David Howells <dhowells@redhat.com>, David Woodhouse <dwmw2@infradead.org>,
        keyrings@vger.kernel.org, linux-kernel@vger.kernel.org
Date: Tue, 26 Apr 2016 23:00:47 +0200
In-Reply-To: <8760v464gr.fsf@rustcorp.com.au>
References: <20160423184421.GL3348@decadent.org.uk>
	 <20160423184501.GM3348@decadent.org.uk> <8760v464gr.fsf@rustcorp.com.au>
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On Tue, 2016-04-26 at 20:07 +0930, Rusty Russell wrote:
> Ben Hutchings <ben@decadent.org.uk> writes:
> >=20
> > Signing a module should only make it trusted by the specific kernel it
> > was built for, not anything else.=C2=A0=C2=A0Loading a signed module me=
ant for a
> > kernel with a different ABI could have interesting effects.
> > Therefore, treat all signatures as invalid when a module is
> > force-loaded.
> >=20
> > Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> > Cc: stable@vger.kernel.org
> > ---
> > =C2=A0kernel/module.c | 13 +++++++++----
> > =C2=A01 file changed, 9 insertions(+), 4 deletions(-)
> >=20
> > 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 s=
truct module *mod,
> > =C2=A0#endif
> > =C2=A0
> > =C2=A0#ifdef CONFIG_MODULE_SIG
> > -static int module_sig_check(struct load_info *info)
> > +static int module_sig_check(struct load_info *info, int flags)
> > =C2=A0{
> > =C2=A0	int err =3D -ENOKEY;
> > =C2=A0	const unsigned long markerlen =3D sizeof(MODULE_SIG_STRING) - 1;
> > =C2=A0	const void *mod =3D info->hdr;
> > =C2=A0
> > -	if (info->len > markerlen &&
> > +	/*
> > +	=C2=A0* Require flags =3D=3D 0, as a module with version information
> > +	=C2=A0* removed is no longer the module that was signed
> > +	=C2=A0*/
> > +	if (flags =3D=3D 0 &&
> This check is a bit lazy.=C2=A0=C2=A0We 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.

--=20
Ben Hutchings
The generation of random numbers is too important to be left to chance.
                                                            - Robert Coveyo=
u
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