linux-kernel - Re: [PATCH 8/8] modules: inherit TAINT_PROPRIETARY

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Date:   Fri, 31 Jul 2020 10:51:30 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 8/8] modules: inherit TAINT_PROPRIETARY_MODULE

+++ Christoph Hellwig [30/07/20 18:29 +0200]:
>On Thu, Jul 30, 2020 at 04:12:32PM +0200, Jessica Yu wrote:
>>> +	if (owner && test_bit(TAINT_PROPRIETARY_MODULE, &owner->taints)) {
>>> +		if (mod->using_gplonly_symbols) {
>>> +			sym = NULL;
>>> +			goto getname;
>>> +		}
>>> +		add_taint_module(mod, TAINT_PROPRIETARY_MODULE,
>>> +				 LOCKDEP_NOW_UNRELIABLE);
>>> +	}
>>
>> Sorry that I didn't think of this yesterday, but I'm wondering if we
>> should print a warning before add_taint_module(). Maybe something
>> along the lines of, "%s: module uses symbols from proprietary module
>> %s, inheriting taint.", with %s being mod->name, owner->name. We can
>> check mod->taints for TAINT_PROPRIETARY_MODULE and print the warning once.
>>
>> Additionally, maybe it's a good idea to print an error before goto
>> getname (e.g., "%s: module using GPL-only symbols uses symbols from
>> proprietary module %s."), so one would know why the module load
>> failed, right now this manifests itself as an unknown symbol error.
>>
>> Otherwise, this patchset looks good to me and I agree with it in
>> principle. Thanks Christoph!
>
>What about this version?  It also factors the code out into a new
>helper, and replaces the add_taint_module with a simple set_bit,
>as the system-wide tain must have been set before by definition:

Yep, this version looks much better. See below for nits.

>---
>>From 25e928b6b691911717d30b3449e56fca3e13dba9 Mon Sep 17 00:00:00 2001
>From: Christoph Hellwig <hch@....de>
>Date: Tue, 28 Jul 2020 23:33:33 +0200
>Subject: modules: inherit TAINT_PROPRIETARY_MODULE
>
>If a TAINT_PROPRIETARY_MODULE exports symbol, inherit the taint flag
>for all modules importing these symbols, and don't allow loading
>symbols from TAINT_PROPRIETARY_MODULE modules if the module previously
>imported gplonly symbols.  Add a anti-circumvention devices so people
>don't accidentally get themselves into trouble this way.
>
>Comment from Greg:
>  "Ah, the proven-to-be-illegal "GPL Condom" defense :)"
>
>Signed-off-by: Christoph Hellwig <hch@....de>
>Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>---
> include/linux/module.h |  1 +
> kernel/module.c        | 26 ++++++++++++++++++++++++++
> 2 files changed, 27 insertions(+)
>
>diff --git a/include/linux/module.h b/include/linux/module.h
>index 30b0f5fcdb3c37..e30ed5fa33a738 100644
>--- a/include/linux/module.h
>+++ b/include/linux/module.h
>@@ -389,6 +389,7 @@ struct module {
> 	unsigned int num_gpl_syms;
> 	const struct kernel_symbol *gpl_syms;
> 	const s32 *gpl_crcs;
>+	bool using_gplonly_symbols;
>
> #ifdef CONFIG_UNUSED_SYMBOLS
> 	/* unused exported symbols. */
>diff --git a/kernel/module.c b/kernel/module.c
>index afb2bfdd5134b3..81d5facce28c14 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -1431,6 +1431,24 @@ static int verify_namespace_is_imported(const struct load_info *info,
> 	return 0;
> }
>
>+static bool inherit_taint(struct module *mod, struct module *owner)
>+{
>+	if (!owner || !test_bit(TAINT_PROPRIETARY_MODULE, &owner->taints))
>+		return true;
>+
>+	if (mod->using_gplonly_symbols) {
>+		pr_info("%s: module using GPL-only symbols uses symbols from proprietary module %s.\n",
>+			mod->name, owner->name);

pr_err() maybe?

>+		return false;
>+	}
>+
>+	if (!test_bit(TAINT_PROPRIETARY_MODULE, &mod->taints)) {
>+		pr_info("%s: module uses symbols from proprietary module %s, inheriting taint.\n",
>+			mod->name, owner->name);

and pr_warn()? But otherwise this looks much better.

Thanks,

Jessica