From: Rusty Russell <rusty@rustcorp.com.au>
To: Ben Hutchings <ben@decadent.org.uk>
Cc: David Howells <dhowells@redhat.com>, David Woodhouse <dwmw2@infradead.org>,
        keyrings@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] module: Invalidate signatures on force-loaded modules
In-Reply-To: <20160423184501.GM3348@decadent.org.uk>
References: <20160423184421.GL3348@decadent.org.uk> <20160423184501.GM3348@decadent.org.uk>
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Date: Tue, 26 Apr 2016 20:07:24 +0930
Message-ID: <8760v464gr.fsf@rustcorp.com.au>
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Ben Hutchings <ben@decadent.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@decadent.org.uk>
> Cc: stable@vger.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?

Cheers,
Rusty.