linux-kernel - Re: BUG: use-after-free bisected to "usb: typec: class: fix typec_altmode_put

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Date: Sun, 24 Dec 2023 13:14:52 +0100
From: "Christian A. Ehrhardt" <lk@...e.de>
To: Chris Bainbridge <chris.bainbridge@...il.com>
Cc: rdbabiera@...gle.com, heikki.krogerus@...ux.intel.com,
	Greg KH <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org
Subject: Re: BUG: use-after-free bisected to "usb: typec: class: fix
 typec_altmode_put_partner to put plugs"


Hi Chris,

[ Cc: linux-usb@...r.kernel.org ]

On Sun, Dec 24, 2023 at 12:54:11AM +0000, Chris Bainbridge wrote:
> Hello,
> 
> A use-after-free error has appeared after a recent commit. This occurs
> when I unplug the USB-C dock (HP G5).
> 
> 
> b17b7fe6dd5c6ff74b38b0758ca799cdbb79e26e is the first bad commit
> commit b17b7fe6dd5c6ff74b38b0758ca799cdbb79e26e
> Author: RD Babiera <rdbabiera@...gle.com>
> Date:   Wed Nov 29 19:23:50 2023 +0000
> 
>     usb: typec: class: fix typec_altmode_put_partner to put plugs

I'm not very familiar with the code in question but the double
free seems rather obvious to me as typec_altmode_put_partner()
frees the altmode itself (which is already being releasee) and not
the partner.

I think this might fix it. Can you give it a try? If it does I can
cook up a proper patch later this week.

     regards    Christian

diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
index 16a670828dde..2da19feacd91 100644
--- a/drivers/usb/typec/class.c
+++ b/drivers/usb/typec/class.c
@@ -263,11 +263,13 @@ static void typec_altmode_put_partner(struct altmode *altmode)
 {
 	struct altmode *partner = altmode->partner;
 	struct typec_altmode *adev;
+	struct typec_altmode *partner_adev;
 
 	if (!partner)
 		return;
 
 	adev = &altmode->adev;
+	partner_adev = &partner->adev;
 
 	if (is_typec_plug(adev->dev.parent)) {
 		struct typec_plug *plug = to_typec_plug(adev->dev.parent);
@@ -276,7 +278,7 @@ static void typec_altmode_put_partner(struct altmode *altmode)
 	} else {
 		partner->partner = NULL;
 	}
-	put_device(&adev->dev);
+	put_device(&partner_adev->dev);
 }
 
 /**