From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753096Ab2APBFV (ORCPT ); Sun, 15 Jan 2012 20:05:21 -0500 Received: from smtp.infotech.no ([82.134.31.41]:52952 "EHLO smtp.infotech.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752207Ab2APBEl (ORCPT ); Sun, 15 Jan 2012 20:04:41 -0500 Message-ID: <4F13779E.1070807@interlog.com> Date: Sun, 15 Jan 2012 20:04:30 -0500 From: Douglas Gilbert Reply-To: dgilbert@interlog.com User-Agent: Mozilla/5.0 (X11; Linux i686; rv:8.0) Gecko/20111124 Thunderbird/8.0 MIME-Version: 1.0 To: Paolo Bonzini CC: linux-kernel@vger.kernel.org, Petr Matousek , Linus Torvalds , linux-scsi@vger.kernel.org, Jens Axboe , James Bottomley Subject: Re: [PATCH v2 0/3] possible privilege escalation via SG_IO ioctl (CVE-2011-4127) References: <1326380489-9044-1-git-send-email-pbonzini@redhat.com> In-Reply-To: <1326380489-9044-1-git-send-email-pbonzini@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12-01-12 10:01 AM, Paolo Bonzini wrote: > Partition block devices or LVM volumes can be sent SCSI commands via > SG_IO, which are then passed down to the underlying device; it's > been this way forever, it was mentioned in 2004 in LKML at > https://lkml.org/lkml/2004/8/12/218 and it is even documented in the > sg_dd man page: > > blk_sgio=1 > when set to 0, block devices (e.g. /dev/sda) are treated > like normal files (i.e. read(2) and write(2) are used for > IO). When set to 1, block devices are assumed to accept the > SG_IO ioctl and SCSI commands are issued for IO. [...] > If the input or output device is a block device partition > (e.g. /dev/sda3) then setting this option causes the > partition information to be ignored (since access is > directly to the underlying device). The ability to use the SG_IO ioctl on a block device was added at the start of the lk 2.6 series. It should have been restricted to non-partition block device nodes (e.g. allowed on /dev/sda, disallowed on /dev/sda3). The successor to sg_dd is called ddpt which will abort a copy when the pass-through (requested by "iflag=pt") is used on a partition node: # ddpt if=/dev/sda3 iflag=pt bs=512 of=/dev/null count=1 >> warning: Size of input block device is different from pt size. >> Pass-through on block partition can give unexpected offsets. >> Abort copy, use iflag=force to override. ddpt is ported to FreeBSD and Win32. The ability to call a pass-through on a partition node is a Linux specific problem. > This is problematic because "safe" SCSI commands, including READ or WRITE, > can be sent to the disk without any particular capability. All that is > required is having a file descriptor for the block device, and permission > to send a ioctl. However, when a user lets a program access /dev/sda2, > it still should not be able to read/write /dev/sda outside the boundaries > of that partition. > > Encryption on the host is a mitigating factor, but it does not provide > a full solution. In particular it doesn't protect against DoS (write > random data), replay attacks (reinstate old ciphertext sectors), or > writes to unencrypted areas including the MBR, the partition table, or > /boot. > > The patches implement a simple global whitelist for both partitions > and partial disk mappings. Patch 1 refactors the code to prepare for > introduction of the whitelist, while patch 2 actually implements it for > the SCSI ioctls. Logical volumes are also affected if they have only one > target, and this target can pass ioctls to the underlying block device. > Patch 3 thus adds the whitelist to logical volumes as well. > > This should be entirely independent of capabilities. Continuing the > previous example, if the same user gives CAP_SYS_RAWIO to the program and > write access to /dev/sdb, the program should be able to send arbitrary > SCSI commands to /dev/sdb, but still should not be able to access /dev/sda > outside the boundaries of /dev/sda2. However, for now when the program > has CAP_SYS_RAWIO the ioctls are let through (while still being logged > to dmesg). > > drivers/ide/ has several ioctls that should only be restricted to the full > block device (for example HDIO_SET_*, HDIO_DRIVE_CMD, HDIO_DRIVE_TASK, > HDIO_DRIVE_RESET). However, all of them require either CAP_SYS_ADMIN > or CAP_SYS_RAWIO, so they do not need any change given the above interim > measure. > > Tested on top of 3.2 + Linus's patch to sanitize ioctl return values. Is that a fixed version of patch at the end of this post: http://marc.info/?l=linux-kernel&m=132578310403616&w=2 The fix being s/ENOIOCTLCMD/-ENOIOCTLCMD/ in is_unrecognized_ioctl() ? If not could you post the patch you are referring to the linux-scsi list. Also could you post "PATCH v2 3/3 ..." to this list as well so we have a complete set? Doug Gilbert