Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752196AbdIVLhm (ORCPT ); Fri, 22 Sep 2017 07:37:42 -0400 Received: from mail-io0-f182.google.com ([209.85.223.182]:47878 "EHLO mail-io0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751928AbdIVLhk (ORCPT ); Fri, 22 Sep 2017 07:37:40 -0400 X-Google-Smtp-Source: AOwi7QDe9CriRIhtiOqr4lbmDYhOiXFscJ8SMKrOUnSpqmCEbCHIlolt0rplBTi0e04PP0UvtxkNkty9WmmN+7X7j+0= MIME-Version: 1.0 In-Reply-To: References: From: Andrey Konovalov Date: Fri, 22 Sep 2017 13:37:38 +0200 Message-ID: Subject: Re: usb/storage/uas: slab-out-of-bounds in uas_probe To: Alan Stern Cc: Greg Kroah-Hartman , Oliver Neukum , USB list , linux-scsi@vger.kernel.org, usb-storage@lists.one-eyed-alien.net, LKML , Dmitry Vyukov , Kostya Serebryany , syzkaller Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4622 Lines: 129 On Thu, Sep 21, 2017 at 9:04 PM, Alan Stern wrote: > On Thu, 21 Sep 2017, Andrey Konovalov wrote: > >> On Thu, Sep 21, 2017 at 6:10 PM, Greg Kroah-Hartman >> wrote: >> > On Thu, Sep 21, 2017 at 05:39:05PM +0200, Andrey Konovalov wrote: >> >> Hi! >> >> >> >> I've got the following report while fuzzing the kernel with syzkaller. >> >> >> >> On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18). >> >> >> >> The issue occurs when we iterate over interface altsettings, but I >> >> don't see the driver doing anything wrong. I might be missing >> >> something, or this might be an issue in USB core altsettings parsing. >> > >> > >> > Any chance you happen to have the descriptors that you were feeding into >> > the kernel at this crash? That might help in figuring out what "went >> > wrong". >> >> Here's the data that I feed into dummy_udc: >> >> 00 00 00 00 09 02 12 00 01 34 05 80 07 09 04 6e >> 09 00 08 06 62 00 12 01 05 00 cb f7 71 83 04 00 >> 05 00 ab f6 07 81 08 01 >> >> Also attaching a C reproducer (requires dummy_hcd and gadgetfs) and my .config. > > Why do your reproducers use an mmap'ed array for their data instead of > a plain old statically allocated array? That's just the way syzkaller generates reproducers, it uses mmap() to allocate memory to feed into syscalls. > > Anyway, this turns out to be a genuine (and subtle!) bug in the uas > driver. The uas_find_uas_alt_setting() routine in uas-detect.h returns > a bAlternateSetting value, but then the uas_use_uas_driver() routine > uses this value as an index to the altsetting array -- which it isn't. > > Normally this doesn't cause any problems because the the entries in the > array have bAlternateSetting values 0, 1, etc., so the value is equal > to the index. But in your fuzzed case, that wasn't true. > > The patch below fixes this bug, by returning a pointer to the > alt-setting entry instead of either the value or the index. Pointers > are less subject to misinterpretation. The patch helps, thanks! Tested-by: Andrey Konovalov > > Alan Stern > > > > Index: usb-4.x/drivers/usb/storage/uas-detect.h > =================================================================== > --- usb-4.x.orig/drivers/usb/storage/uas-detect.h > +++ usb-4.x/drivers/usb/storage/uas-detect.h > @@ -9,7 +9,8 @@ static int uas_is_interface(struct usb_h > intf->desc.bInterfaceProtocol == USB_PR_UAS); > } > > -static int uas_find_uas_alt_setting(struct usb_interface *intf) > +static struct usb_host_interface *uas_find_uas_alt_setting( > + struct usb_interface *intf) > { > int i; > > @@ -17,10 +18,10 @@ static int uas_find_uas_alt_setting(stru > struct usb_host_interface *alt = &intf->altsetting[i]; > > if (uas_is_interface(alt)) > - return alt->desc.bAlternateSetting; > + return alt; > } > > - return -ENODEV; > + return NULL; > } > > static int uas_find_endpoints(struct usb_host_interface *alt, > @@ -58,14 +59,14 @@ static int uas_use_uas_driver(struct usb > struct usb_device *udev = interface_to_usbdev(intf); > struct usb_hcd *hcd = bus_to_hcd(udev->bus); > unsigned long flags = id->driver_info; > - int r, alt; > - > + struct usb_host_interface *alt; > + int r; > > alt = uas_find_uas_alt_setting(intf); > - if (alt < 0) > + if (!alt) > return 0; > > - r = uas_find_endpoints(&intf->altsetting[alt], eps); > + r = uas_find_endpoints(alt, eps); > if (r < 0) > return 0; > > Index: usb-4.x/drivers/usb/storage/uas.c > =================================================================== > --- usb-4.x.orig/drivers/usb/storage/uas.c > +++ usb-4.x/drivers/usb/storage/uas.c > @@ -873,14 +873,14 @@ MODULE_DEVICE_TABLE(usb, uas_usb_ids); > static int uas_switch_interface(struct usb_device *udev, > struct usb_interface *intf) > { > - int alt; > + struct usb_host_interface *alt; > > alt = uas_find_uas_alt_setting(intf); > - if (alt < 0) > - return alt; > + if (!alt) > + return -ENODEV; > > - return usb_set_interface(udev, > - intf->altsetting[0].desc.bInterfaceNumber, alt); > + return usb_set_interface(udev, alt->desc.bInterfaceNumber, > + alt->desc.bAlternateSetting); > } > > static int uas_configure_endpoints(struct uas_dev_info *devinfo) >