From patchwork Sat Jan 1 02:07:12 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alan Stern X-Patchwork-Id: 529541 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04BA9C433F5 for ; Sat, 1 Jan 2022 02:07:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231920AbiAACHN (ORCPT ); Fri, 31 Dec 2021 21:07:13 -0500 Received: from netrider.rowland.org ([192.131.102.5]:58063 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S231877AbiAACHN (ORCPT ); Fri, 31 Dec 2021 21:07:13 -0500 Received: (qmail 1142479 invoked by uid 1000); 31 Dec 2021 21:07:12 -0500 Date: Fri, 31 Dec 2021 21:07:12 -0500 From: Alan Stern To: Greg KH Cc: USB mailing list , Kernel development list , syzkaller-bugs@googlegroups.com Subject: [PATCH] USB: Fix "slab-out-of-bounds Write" bug in usb_hcd_poll_rh_status Message-ID: References: <00000000000060560805d4773ba0@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <00000000000060560805d4773ba0@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org When the USB core code for getting root-hub status reports was originally written, it was assumed that the hub driver would be its only caller. But this isn't true now; user programs can use usbfs to communicate with root hubs and get status reports. When they do this, they may use a transfer_buffer that is smaller than the data returned by the HCD, which will lead to a buffer overflow error when usb_hcd_poll_rh_status() tries to store the status data. This was discovered by syzbot: BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:225 [inline] BUG: KASAN: slab-out-of-bounds in usb_hcd_poll_rh_status+0x5f4/0x780 drivers/usb/core/hcd.c:776 Write of size 2 at addr ffff88801da403c0 by task syz-executor133/4062 This patch fixes the bug by reducing the amount of status data if it won't fit in the transfer_buffer. If some data gets discarded then the URB's completion status is set to -EOVERFLOW rather than 0, to let the user know what happened. Reported-and-tested-by: syzbot+3ae6a2b06f131ab9849f@syzkaller.appspotmail.com Signed-off-by: Alan Stern Cc: --- [as1966] drivers/usb/core/hcd.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) Index: usb-devel/drivers/usb/core/hcd.c =================================================================== --- usb-devel.orig/drivers/usb/core/hcd.c +++ usb-devel/drivers/usb/core/hcd.c @@ -753,6 +753,7 @@ void usb_hcd_poll_rh_status(struct usb_h { struct urb *urb; int length; + int status; unsigned long flags; char buffer[6]; /* Any root hubs with > 31 ports? */ @@ -770,11 +771,17 @@ void usb_hcd_poll_rh_status(struct usb_h if (urb) { clear_bit(HCD_FLAG_POLL_PENDING, &hcd->flags); hcd->status_urb = NULL; + if (urb->transfer_buffer_length >= length) { + status = 0; + } else { + status = -EOVERFLOW; + length = urb->transfer_buffer_length; + } urb->actual_length = length; memcpy(urb->transfer_buffer, buffer, length); usb_hcd_unlink_urb_from_ep(hcd, urb); - usb_hcd_giveback_urb(hcd, urb, 0); + usb_hcd_giveback_urb(hcd, urb, status); } else { length = 0; set_bit(HCD_FLAG_POLL_PENDING, &hcd->flags);