Re: [PATCH 8/8] modules: inherit TAINT_PROPRIETARY_MODULE

From: Jessica Yu
Date: Fri Jul 31 2020 - 04:51:39 EST


+++ 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@xxxxxx>
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@xxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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