[PATCH] init, allow blacklisting of module_init functions

[PATCH] init, allow blacklisting of module_init functions

[Prarit Bhargava]

At some point I was 100% sure this worked.  I do remember testing it against
just a loadable module and had positive testing results.  I went back to
the time that it was commited (3.15-ish) and blacklisting a module init
function didn't work there either, so something went wrong somewhere.  In
any case this is a trivial patch to add the functionality...

P.

---8<---

sprint_symbol_no_offset() returns the string "function_name [module_name]"
where [module_name] is not printed for built in kernel functions.  This
means that the blacklisting code will fail when comparing module function
names with the extended string.  This patch adds the functionality to
block a module's module_init() function by finding the space in the string
and truncating the comparison to that length.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yang Shi <yang.shi@linaro.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 init/main.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/init/main.c b/init/main.c
index 4c17fda5c2ff..730d6a846216 100644
--- a/init/main.c
+++ b/init/main.c
@@ -708,14 +708,25 @@ static bool __init_or_module initcall_blacklisted(initcall_t fn)
 {
 	struct blacklist_entry *entry;
 	char fn_name[KSYM_SYMBOL_LEN];
+	char *space;
+	int length;
 
 	if (list_empty(&blacklisted_initcalls))
 		return false;
 
 	sprint_symbol_no_offset(fn_name, (unsigned long)fn);
+	/*
+	 * fn will be "function_name [module_name]" where [module_name] is not
+	 * displayed for built-in init functions.  Strip off the [module_name].
+	 */
+	space = strchrnul(fn_name, ' ');
+	if (!space)
+		length = strlen(fn_name);
+	else
+		length = space - fn_name;
 
 	list_for_each_entry(entry, &blacklisted_initcalls, next) {
-		if (!strcmp(fn_name, entry->buf)) {
+		if (!strncmp(fn_name, entry->buf, length)) {
 			pr_debug("initcall %s blacklisted\n", fn_name);
 			return true;
 		}
-- 
1.7.9.3

Re: [PATCH] init, allow blacklisting of module_init functions

[Rasmus Villemoes]

On Wed, Jun 15 2016, Prarit Bhargava <prarit@redhat.com> wrote:

> At some point I was 100% sure this worked.  I do remember testing it against
> just a loadable module and had positive testing results.

I think the current %ps/%pf behaviour was introduced in 4796dd200db9
(way back in 2012). 

> In any case this is a trivial patch to add the functionality...

Which I still think is broken and needlessly complicated. Please read my
first reply again.

Rasmus

Re: [PATCH] init, allow blacklisting of module_init functions

[Prarit Bhargava]

On 06/15/2016 04:25 PM, Rasmus Villemoes wrote:
> On Wed, Jun 15 2016, Prarit Bhargava <prarit@redhat.com> wrote:
> 
>> At some point I was 100% sure this worked.  I do remember testing it against
>> just a loadable module and had positive testing results.
> 
> I think the current %ps/%pf behaviour was introduced in 4796dd200db9
> (way back in 2012). 

Yeah, I'm scratching my head on that.  I *know* I tested it and it worked.

> 
>> In any case this is a trivial patch to add the functionality...
> 
> Which I still think is broken and needlessly complicated. Please read my
> first reply again.
> 

Oops -- I completely missed the 2nd half of your reply.  Sorry 'bout that.

I'll do a v3 in a bit

P.
> Rasmus
>