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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.0585 Linux: backends treating grant mapping errors as bugs 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-2021-26931 Original Bulletin: http://xenbits.xen.org/xsa/advisory-362.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-2021-26931 / XSA-362 version 3 Linux: backends treating grant mapping errors as bugs UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= Block, net, and SCSI backends consider certain errors a plain bug, deliberately causing a kernel crash. For errors potentially being at least under the influence of guests, like out of memory conditions, it isn't correct to assume so. Memory allocations potentially causing such crashes occur only when Linux is running in PV mode, though. IMPACT ====== A malicious or buggy frontend driver may be able to crash the corresponding backend driver, potentially affecting the entire domain running the backend driver. VULNERABLE SYSTEMS ================== Linux versions from at least 2.6.39 onwards are vulnerable, when run in PV mode. Earlier versions differ significantly in behavior and may therefore instead surface other issues under the same conditions. Linux run in HVM / PVH modes is not vulnerable. MITIGATION ========== For Linux, running the backends in HVM or PVH domains will avoid the vulnerability. For protocols where non-Linux-kernel based backends are available, reconfiguring guests to use alternative (e.g. qemu-based) backends may allow to avoid the vulnerability. In all other cases there is no known mitigation. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patches resolves this issue. Applying the attached patches resolves this issue. xsa362-linux-1.patch Linux 5.11-rc - 5.10 xsa362-linux-2.patch Linux 5.11-rc - 3.16 xsa362-linux-3.patch Linux 5.11-rc - 4.1 $ sha256sum xsa362* d64334807f16ff9909503b3cc9b8b93fd42d2c36e1fb0e508b89a765a53071a8 xsa362-linux-1.patch b6d02952e7fbede55b868cb2dc4d8853284996883dc72518a0cd5b14d6c7fdd4 xsa362-linux-2.patch 0a2661380d8f786fefe12e5a8b1528d4a79f1ad058c26b417c52449a7e16a302 xsa362-linux-3.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/UMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZszQH/jwCgehGBbejtpFjiOqEPdqIQhd0X+Q1feFD9PB6 07gfGanmSds5mitr0ezTHbfLw85CoFbAJhalNdx9XeQrZTIvRAizkCi779rE9UYZ H0CN73GoObF4E8q+tVRpZni0Rcnb77bETRsmlYjRYRjtZNZ1+7vbn4tf4JMccoo0 qhz1/bqY3e4yHPcdxb9P3T/DQKNG+nJjkn4kNueYo1PUGUetxw6HXbXWHh6WvbOr mfd+sTxRSf+Nk2OZhtofjIYEIeL058axZoSuARBIPphBmOCumUTGzrypZwe5BTuF GMQqlguxPU0rFscGd/Js05suFhQQR4ccJlSGRs7pswt9i0M= =KnG3 - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. 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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). 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