[PATCH] kobject: Don't trigger kobject_uevent(KOBJ_REMOVE) twice.

[Tetsuo Handa]

syzbot is hitting use-after-free bug in uinput module [1]. This is because
kobject_uevent(KOBJ_REMOVE) is called again due to commit 0f4dafc0563c6c49
("Kobject: auto-cleanup on final unref") after memory allocation fault
injection made kobject_uevent(KOBJ_REMOVE) from device_del() from
input_unregister_device() fail, while uinput_destroy_device() is expecting
that kobject_uevent(KOBJ_REMOVE) is not called after device_del() from
input_unregister_device() completed. Fix this problem by marking "remove"
event done regardless of result.

[1] https://syzkaller.appspot.com/bug?id=8b17c134fe938bbddd75a45afaa9e68af43a362d

Reported-by: syzbot <syzbot+f648cfb7e0b52bf7ae32@xxxxxxxxxxxxxxxxxxxxxxxxx>
Analyzed-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Cc: Kay Sievers <kay@xxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 lib/kobject_uevent.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index f058026..7ec4165 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -466,6 +466,13 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 	int i = 0;
 	int retval = 0;
 
+	/*
+	 * Mark "remove" event done regardless of result, for some subsystems
+	 * do not want to re-trigger "remove" event via automatic cleanup.
+	 */
+	if (action == KOBJ_REMOVE && kobj->state_add_uevent_sent)
+		kobj->state_remove_uevent_sent = 1;
+
 	pr_debug("kobject: '%s' (%p): %s\n",
 		 kobject_name(kobj), kobj, __func__);
 
@@ -567,10 +574,6 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 		kobj->state_add_uevent_sent = 1;
 		break;
 
-	case KOBJ_REMOVE:
-		kobj->state_remove_uevent_sent = 1;
-		break;
-
 	case KOBJ_UNBIND:
 		zap_modalias_env(env);
 		break;
-- 
1.8.3.1