3.16.74-rc1 review patch. If anyone has any objections, please let me know.
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From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp
commit c03a0fd0b609e2f5c669c2b7f27c8e1928e9196e upstream.
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.
That commit intended to catch cases where nobody even attempted to send "remove" uevents. But there is no guarantee that an event will ultimately be sent. We are at the point of no return as far as the rest of the kernel is concerned; there are no repeats or do-overs.
Also, it is not clear whether some subsystem depends on that commit. If no subsystem depends on that commit, it will be better to remove the state_{add,remove}_uevent_sent logic. But we don't want to risk a regression (in a patch which will be backported) by trying to remove that logic. Therefore, as a first step, let's avoid the use-after-free bug by making sure that kobject_uevent(KOBJ_REMOVE) won't be triggered twice.
[1] https://syzkaller.appspot.com/bug?id=8b17c134fe938bbddd75a45afaa9e68af43a362...
Reported-by: syzbot syzbot+f648cfb7e0b52bf7ae32@syzkaller.appspotmail.com Analyzed-by: Dmitry Torokhov dmitry.torokhov@gmail.com Fixes: 0f4dafc0563c6c49 ("Kobject: auto-cleanup on final unref") Cc: Kay Sievers kay@vrfy.org Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/lib/kobject_uevent.c +++ b/lib/kobject_uevent.c @@ -178,6 +178,13 @@ int kobject_uevent_env(struct kobject *k struct uevent_sock *ue_sk; #endif
+ /* + * 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_remove_uevent_sent = 1; + pr_debug("kobject: '%s' (%p): %s\n", kobject_name(kobj), kobj, __func__);
@@ -275,8 +282,6 @@ int kobject_uevent_env(struct kobject *k */ if (action == KOBJ_ADD) kobj->state_add_uevent_sent = 1; - else if (action == KOBJ_REMOVE) - kobj->state_remove_uevent_sent = 1;
mutex_lock(&uevent_sock_mutex); /* we will send an event, so request a new sequence number */