Re: [PATCH v0 00/42] notifiers: Return an error when callback is already registered

Borislav Petkov
2021-11-08T14:36:02Z

On Mon, Nov 08, 2021 at 03:24:39PM +0100, Borislav Petkov wrote:
> I guess I can add another indirection to notifier_chain_register() and
> avoid touching all the call sites.

IOW, something like this below.

This way I won't have to touch all the callsites and the registration
routines would still return a proper value instead of returning 0
unconditionally.

---
diff --git a/kernel/notifier.c b/kernel/notifier.c
index b8251dc0bc0f..04f08b2ef17f 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -19,14 +19,12 @@ BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);
* are layered on top of these, with appropriate locking added.
*/

-static int notifier_chain_register(struct notifier_block **nl,
- struct notifier_block *n)
+static int __notifier_chain_register(struct notifier_block **nl,
+ struct notifier_block *n)
{
while ((*nl) != NULL) {
- if (unlikely((*nl) == n)) {
- WARN(1, "double register detected");
- return 0;
- }
+ if (unlikely((*nl) == n))
+ return -EEXIST;
if (n->priority > (*nl)->priority)
break;
nl = &((*nl)->next);
@@ -36,6 +34,18 @@ static int notifier_chain_register(struct notifier_block **nl,
return 0;
}

+static int notifier_chain_register(struct notifier_block **nl,
+ struct notifier_block *n)
+{
+ int ret = __notifier_chain_register(nl, n);
+
+ if (ret == -EEXIST)
+ WARN(1, "double register of notifier callback %ps detected",
+ n->notifier_call);
+
+ return ret;
+}
+
static int notifier_chain_unregister(struct notifier_block **nl,
struct notifier_block *n)
{

--
Regards/Gruss,
Boris.