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

From: Tetsuo Handa
Date: Wed Feb 20 2019 - 08:38:49 EST


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