Date: Wed, 13 Jan 2021 16:40:06 +0100 From: Marcus Meissner <meissner@...e.de> To: oss-security@...ts.openwall.com Subject: Re: CVE-2020-28374: Linux SCSI target (LIO) unrestricted copy offload Hi, For tcmu-runner Mitre suggested that we use a different CVE as its not the same codebase. Please use CVE-2021-3139 for tcmu-runner. Ciao, Marcus On Tue, Jan 12, 2021 at 07:01:34PM +0100, David Disseldorp wrote: > =============================================================================== > == Subject: Linux SCSI target (LIO) unrestricted copy offload > == > == > == CVE ID#: CVE-2020-28374 > == > == Versions: Linux: v3.12 and later > == tcmu-runner: v1.3.0 and later > == > == Summary: An attacker with access to a LUN and knowledge of Unit Serial > == Number assignments can read and write to any LIO backstore, > == regardless of SCSI transport settings. > =============================================================================== > > > Description > ----------- > SCSI "EXTENDED COPY" (XCOPY) requests sent to a Linux SCSI target (LIO) allow an > attacker to read or write anywhere on any LIO backstore configured on the > host, provided the attacker has access to one LUN and knowledge of the victim > backstore's vpd_unit_serial (AKA "wwn"). This is possible regardless of the > transport/HBA settings for the victim backstore. > - with vhost-scsi this can allow VM guests to read or write to images assigned > to other qemu processes > - with iSCSI this allows CHAP, ACL and network portal isolation bypass > - backstores with no corresponding transport LUN mapping remain vulnerable > - all other LIO transports and backstores which allow for XCOPY processing by > LIO's target_core_xcopy handler should be considered vulnerable > - tcmu-runner based user backstores are also vulnerable via a similar logic bug > > This is due to the way that LIO behaves when processing XCOPY > copy-source/copy-destination (CSCD) descriptors; when attempting to match > CSCD descriptors with corresponding se_devices, target_xcopy_locate_se_dev_e4() > iterates over LIO's global devices list, which includes all configured > backstores, instead of only considering backstores which are exposed to the > initiator via transport layer ACL settings. > > Similarly, when LIO is configured to forward SCSI requests to the user-space > tcmu-runner daemon (via target_core_user), tcmu-runner's xcopy_locate_udev() > iterates over all tcmu-runner devices, without considering any transport layer > restrictions. > > > Exploitation > ------------ > The attacker sends an XCOPY request with two CSCD descriptors. > One CSCD descriptor must correspond to the NAA IEEE identifier for the LUN to > which the attacker has access. The other (victim) CSCD descriptor must be an > NAA IEEE identifier which matches another configured backstore within LIO's > global device inventory. > > For successful exploitation of this bug an attacker must be able to provide a > matching NAA identifier for the victim backstore. > > > Affected Versions > ----------------- > Linux Kernel (LIO target_core_xcopy) > - Exploitable as of > f99715ac8d6f ("target: Enable global EXTENDED_COPY setup/release") > + mainline v3.12-rc1 and later > > tcmu-runner (user-space SCSI target, coupled with LIO's target_core_user) > - Exploitable as of 9c86bd0db97a ("tcmur: Add emulate XCOPY command support") > + tcmu-runner v1.3.0 and later > > > Relevance > --------- > Linux kernel LIO deployments are affected under the following conditions: > - Linux kernel with f99715ac8d6f, i.e. mainline v3.12-rc1 or later > - LIO SCSI target (target_core_mod) loaded > - at least two configured backstores > - one "attacker backstore" must be exposed via a SCSI transport (e.g. iSCSI) > which permits access to a potential attacker > + the attacker backstore must allow and use in-kernel LIO XCOPY command > emulation > - all backstores except special "pscsi" passthrough and "user" types > - emulate_3pc=1 must be set (default) > - one or more "victim backstores" must be configured > + transport settings for victim backstores are irrelevant > + all backstore types are vulnerable, including "iblock", "fileio", "rd_mcp", > "pscsi" and "user" > + emulate_3pc=1 must be set the victim backstore (default) > > tcmu-runner deployments are affected under the following conditions: > - tcmu-runner with 9c86bd0db97a, i.e. v1.3.0 or later > - one "attacker backstore" must be exposed via a SCSI transport (e.g. iSCSI) > which permits access to a potential attacker > - one or more "victim backstores" must be configured > + transport settings for victim backstores are irrelevant > + the victim backstore must also be managed by the same tcmu-runner instance > - e.g. an XCOPY request to a "user"+tcmu-runner backstore can't be used to > read or write to an "iblock" backstore, only to other backstores handled > by the same tcmu-runner instance. > > > Mitigation > ---------- > Caveat: instructions below do *not* affect XCOPY requests sent to tcmu-runner > based backstores. They are only suitable for disabling kernel > (target_core_xcopy) support for XCOPY requests. > > Requires acb3f2600eb8 ("target: Reject EXTENDED_COPY when emulate_3pc is disabled") > - v3.12-rc7 or later > > XCOPY support is enabled by default, but can be disabled via: > echo 0 > /sys/kernel/config/target/core/<backstore>/<name>/attrib/emulate_3pc > or > targetcli /backstores/<backstore>/<name> set attribute emulate_3pc=0 > > ...where <backstore> and <name> should be filled appropriately. > > > Fixes > ----- > Linux kernel and tcmu-runner fixes will be provided following the coordinated > release date: 2021-01-12 10:00 Pacific Standard Time. > > > Credits > ------- > Research and patches by David Disseldorp of SUSE. > Patch review by Mike Christie of Oracle, and Lee Duncan of SUSE. > -- Marcus Meissner,SUSE LINUX GmbH; Maxfeldstrasse 5; D-90409 Nuernberg; Zi. 3.1-33,+49-911-740 53-432,,serv=loki,mail=wotan,type=real <meissner@...e.de>
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