Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.0586 Linux: grant mapping error handling issues 17 February 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Linux Kernel Publisher: Xen Operating System: Xen Linux variants Impact/Access: Denial of Service -- Unknown/Unspecified Resolution: Patch/Upgrade CVE Names: CVE-2021-26932 Original Bulletin: http://xenbits.xen.org/xsa/advisory-361.html Comment: This advisory references vulnerabilities in the Linux kernel that also affect distributions other than Xen. It is recommended that administrators running Linux check for an updated version of the kernel for their system. - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2021-26932 / XSA-361 version 4 Linux: grant mapping error handling issues UPDATES IN VERSION 4 ==================== Public release. ISSUE DESCRIPTION ================= Grant mapping operations often occur in batch hypercalls, where a number of operations are done in a single hypercall, the success or failure of each one reported to the backend driver, and the backend driver then loops over the results, performing follow-up actions based on the success or failure of each operation. Unfortunately, when running in PV mode, the Linux backend drivers mishandle this: Some errors are ignored, effectively implying their success from the success of related batch elements. In other cases, errors resulting from one batch element lead to further batch elements not being inspected, and hence successful ones to not be possible to properly unmap upon error recovery. IMPACT ====== A malicious or buggy frontend driver may be able to crash the corresponding backend driver, causing a denial of service potentially affecting the entire domain running the backend driver. A malicious or buggy frontend driver may be able to cause resource leaks in the domain running the corresponding backend driver, leading to a denial of service. VULNERABLE SYSTEMS ================== All Linux versions back to at least 3.2 are vulnerable, when running in PV mode on x86 or when running on Arm. On x86, only systems with Linux backends running in PV mode are vulnerable. Linux backends run in HVM / PVH modes are not vulnerable. MITIGATION ========== On x86, running the backends in HVM or PVH domains will avoid the vulnerability. For protocols where other, e.g. non-kernel-based backends are available, reconfiguring guests to use alternative (e.g. qemu-based) backends may allow to avoid the vulnerability as long as these backends don't rely on similar functionality provided by the xen-gntdev (/dev/gntdev) driver. In all other cases there is no known mitigation. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the attached patches resolves this issue. xsa361-linux-1.patch Linux 5.11-rc - 3.19 xsa361-linux-2.patch Linux 5.11-rc - 3.15 xsa361-linux-3.patch Linux 5.11-rc - 4.19 xsa361-linux-4.patch Linux 5.11-rc - 4.19 xsa361-linux-5.patch Linux 5.11-rc - 4.4 $ sha256sum xsa361* bb00ab6319b4fc536566af50c73e064f10f8b99eaa6b0f0b35a8d174c285a905 xsa361-linux-1.patch 73b6a54aa3773ce11f0de6b9aa1d80dd7f4c297dc71924b1a3886bc3b99ac859 xsa361-linux-2.patch 8e554cfab8cdb4fe1b74601a9432ea4c570f74a952ad757f9294ba1666cbeaea xsa361-linux-3.patch 8c290895d10fc148f99e2a6587811b3037f29c3a0201d69d448ff520cea6f96d xsa361-linux-4.patch 231ae3e1b9bec1b75dbbbee4b5acff620ef7ac2853332aa7b3c4957c6ca7f341 xsa361-linux-5.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches described above (or others which are substantially similar) is permitted during the embargo, even on public-facing systems with untrusted guest users and administrators. Deployment of the mitigation to switch to HVM / PVH backend domains is also permitted during the embargo, even on public-facing systems with untrusted guest users and administrators. HOWEVER, deployment of the non-kernel-based backends mitigation described above is NOT permitted during the embargo on public-facing systems with untrusted guest users and administrators. This is because such a configuration change may be recognizable by the affected guests. AND: Distribution of updated software is prohibited (except to other members of the predisclosure list). Predisclosure list members who wish to deploy significantly different patches and/or mitigations, please contact the Xen Project Security Team. (Note: this during-embargo deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable. This is to enable the community to have oversight of the Xen Project Security Team's decisionmaking.) For more information about permissible uses of embargoed information, consult the Xen Project community's agreed Security Policy: http://www.xenproject.org/security-policy.html - -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmAru/QMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZmFkH/Ay1RoZbbcA4ywdhy9xdnpt0DHMFLjZSbE4sNTi+ J+m9rn69UTK01VDD0RUohTcmWO0nv8ZD+jKETsSq31GiYhVk7XnSmCJkzILGujr8 cf+7jUWWJPcqBmN7xcLBaor9lhpKfMpYlMLBG7twIRHfqOSw6Sm+iD4YC23nkGKF Cb8tpkYCpX3dPMMP74nX00Wta2rqd1BrpAGvAnt9hrHIBfTcpwWE8A4H1eFL/7Dv 5+pVvrSMkyzaR5kI/QBeriXsuOP509CiafUBpeXU85pGWpLgZAqD+puodEVQ2fpT /MqATdNRhgnCzqSqh/ElN/1ZdB7406DbdCnErJiyDdN/OCE= =DUXr - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBYCyyKuNLKJtyKPYoAQhO7A//WNtfNclzv0mWexabbeIM8HwkoiLvp9YJ MGThiV7wENHQODnwzurxRmzZexmRRE4isVMtnM0yeRzDU+0Ik5PRDyMXtCBTnv87 16dNVq6bDhwJ3de7s6MCTH9kSqJR4GXcYfwuRK2BFphw8nfsb4GKK8bVnwkioGXA a70w98ijILbdHgWcIJCOEWtDx3o7olxu5s9cDhgZVYD87S3raKCN+Oof1bi2Rx3j vmP6SZJnH1w5A3Ou83fRyTHCN5d9BkrC8gL6RnsnGnm2Ws9V2EUvjRrV+JtqZ/Qg SV/k7fB+zijDv+EIqi8WyAn/N7/OvvZJBT1RyzmL2YFulluLBKHVzqSoQFI4HP+C oNoCANkMJQUSmjKxnq9rBGEKHsx7WGbRVLBHw8NQw9w7x7ZRd3jT30dDKxmkYRvs EBh0r2OTkPC0cZPy616Nu2oLbR2xZBhiCRPIWB+8EroWu7T3qR5CMZ1IFQ+K5Rnr COFTE86aWsSiQNdTenCfBh7/hIPrMB9S4HMAcF82RAcDlnu+U7KokCc3S8aMy3Jj Xbf0DCLBEcpCrNvNW/1LPwXMTq4rS+DJq7Fk1CBIQGOVk1dGiqmmYssQJ+77s8fB vbL2uTKj1LNpYVJfTBJV4tzZ90jIGqxfVHmW32+rOZE6232HjQ7GvTW27FdPH9y+ nelGuipMt+o= =csqM -----END PGP SIGNATURE-----