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Date: Thu, 14 Apr 2022 12:58:58 +0200 From: Lukas Wunner <lukas@...ner.de> To: Oliver Neukum <oneukum@...e.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org> Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Jann Horn <jannh@...gle.com>, Oleksij Rempel <o.rempel@...gutronix.de>, netdev@...r.kernel.org, linux-usb@...r.kernel.org, Andrew Lunn <andrew@...n.ch>, Eric Dumazet <edumazet@...gle.com>, Jacky Chou <jackychou@...x.com.tw>, Willy Tarreau <w@....eu>, Lino Sanfilippo <LinoSanfilippo@....de>, Philipp Rosenberger <p.rosenberger@...bus.com>, Heiner Kallweit <hkallweit1@...il.com> Subject: Re: [PATCH] usbnet: Fix use-after-free on disconnect On Wed, Apr 13, 2022 at 08:59:48PM +0200, Oliver Neukum wrote: > On 13.04.22 16:16, Lukas Wunner wrote: > > Jann Horn reports a use-after-free on disconnect of a USB Ethernet > > (ax88179_178a.c). Oleksij Rempel has witnessed the same issue with a > > different driver (ax88172a.c). > > I see. Very good catch > > > --- a/drivers/net/usb/usbnet.c > > +++ b/drivers/net/usb/usbnet.c > > @@ -469,6 +469,9 @@ static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb, > > */ > > void usbnet_defer_kevent (struct usbnet *dev, int work) > > { > > + if (dev->intf->condition == USB_INTERFACE_UNBINDING) > > + return; > > But, no, you cannot do this. This is a very blatant layering violation. > You cannot use states internal to usb core like that in a driver. Why do you think it's internal? enum usb_interface_condition is defined in include/linux/usb.h for everyone to see and use. If it was meant to be private, I'd expect it to be marked as such or live in drivers/usb/core/usb.h. Adding Greg to clarify. > I see two options. > 1. A dedicated flag in usbnet (then please with the correct smp barriers) > 2. You introduce an API to usb core to query this. I'd definitely prefer option 2 as I'd hate to duplicate functionality. What do you have in mind? A simple accessor to return intf->condition or something like usb_interface_unbinding() which returns a bool? Thanks, Lukas
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