From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EEB26C76194 for ; Thu, 25 Jul 2019 09:34:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B48152084D for ; Thu, 25 Jul 2019 09:34:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390561AbfGYJeC (ORCPT ); Thu, 25 Jul 2019 05:34:02 -0400 Received: from mx2.suse.de ([195.135.220.15]:52260 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2390537AbfGYJeB (ORCPT ); Thu, 25 Jul 2019 05:34:01 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 8EC60ABE9; Thu, 25 Jul 2019 09:34:00 +0000 (UTC) Message-ID: <1564047229.4670.14.camel@suse.com> Subject: Re: KASAN: use-after-free Read in usbhid_power From: Oliver Neukum To: Alan Stern Cc: andreyknvl@google.com, syzkaller-bugs@googlegroups.com, syzbot , linux-usb@vger.kernel.org Date: Thu, 25 Jul 2019 11:33:49 +0200 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Am Mittwoch, den 24.07.2019, 17:02 -0400 schrieb Alan Stern: > On Wed, 24 Jul 2019, Oliver Neukum wrote: > > > drivers/hid/usbhid/hid-core.c | 13 +++++++++++++ > > 1 file changed, 13 insertions(+) > > > > diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c > > index c7bc9db5b192..98b996ecf4d3 100644 > > --- a/drivers/hid/usbhid/hid-core.c > > +++ b/drivers/hid/usbhid/hid-core.c > > @@ -1229,6 +1229,17 @@ static int usbhid_power(struct hid_device *hid, int lvl) > > struct usbhid_device *usbhid = hid->driver_data; > > int r = 0; > > > > + spin_lock_irq(&usbhid->lock); > > + if (test_bit(HID_DISCONNECTED, &usbhid->iofl)) { > > + r = -ENODEV; > > + spin_unlock_irq(&usbhid->lock); > > + goto bail_out; > > + } else { > > + /* protect against disconnect */ > > + usb_get_dev(interface_to_usbdev(usbhid->intf)); > > + spin_unlock_irq(&usbhid->lock); > > + } > > + > > switch (lvl) { > > case PM_HINT_FULLON: > > r = usb_autopm_get_interface(usbhid->intf); > > @@ -1238,7 +1249,9 @@ static int usbhid_power(struct hid_device *hid, int lvl) > > usb_autopm_put_interface(usbhid->intf); > > break; > > } > > + usb_put_dev(interface_to_usbdev(usbhid->intf)); > > > > +bail_out: > > return r; > > } > > Isn't this treating the symptom instead of the cause? Sort of. Holding a reference for the whole time would have merit, but I doubt it is strictly necessary. > Shouldn't the hid_device hold a reference to usbhid->intf throughout > its lifetime? That way this sort of problem wouldn't arise in any > routine, not just usbhid_power(). Unfortunately the semantics would still be wrong without the check in corner cases. In case disconnect() is called without a physical unplug, we must not touch the power state. I am indeed afraid that in that case my putative fix is still racy. But I don't to just introduce a mutex just for this. Any ideas? Regards Oliver