Headline
CVE-2022-23040
Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn’t check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2022-23036,CVE-2022-23037,CVE-2022-23038,CVE-2022-23039,CVE-2022-23040,CVE-2022-23041,CVE-2022-23042 / XSA-396 version 3 Linux PV device frontends vulnerable to attacks by backends UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn’t check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042 IMPACT ====== Due to race conditions and missing tests of return codes in the Linux PV device frontend drivers a malicious backend could gain access (read and write) to memory pages it shouldn’t have, or it could directly trigger Denial of Service (DoS) in the guest. VULNERABLE SYSTEMS ================== All Linux guests using PV devices are vulnerable in case potentially malicious PV device backends are being used. MITIGATION ========== There is no mitigation available other than not using PV devices in case a backend is suspected to be potentially malicious. RESOLUTION ========== Applying the attached patches resolves this issue. xsa396-linux-*.patch Linux upstream $ sha256sum xsa396* d21d2d2c499d8e7c1cbc347d9df118b27af7d7c9ca5c104fcf1fef022ba6b92d xsa396-linux-01.patch c150c7873497b4d9807fcfe2a4a4831b033597db3d4c3dfaada1e647db1395fa xsa396-linux-02.patch 6439ac16b6d6b29d6773d00895776a7392a321caa01f569062c4140d3d66167c xsa396-linux-03.patch 2cc0b472514be47690ef257ab8d296bbec1827d18f98e1f1bbbfea53aafec78c xsa396-linux-04.patch cd6b6e65fe9915f98b04363bf1f22ddbd7c448215d52858ad1a2318bb1f034c8 xsa396-linux-05.patch 353e4de564897ad07120b17aa7a6a22b90fba6e65f39c20fe561ba06405656f3 xsa396-linux-06.patch bf923c3bc92a908215d5ade016d27f56d1e445da88b04e1e1d4530ea5b139be3 xsa396-linux-07.patch 0a306ed20e4259e2a3583bfab14672a245bd33b24e95e5df8bfc30a25f7e18c6 xsa396-linux-08.patch 130b8305ba8c10e2942553078b845899ef79c5570692a499569a526b1e39d4fe xsa396-linux-09.patch 1f70bdc0a5c1ff1b538d8cbec17e99af5888669f3a33ad8a02d2026719ad4bc9 xsa396-linux-10.patch 48fd782c6b0b705ccb59885d0e1562873f44478ea87f705f08ce18336bc19257 xsa396-linux-11.patch d720350d36f7434e2cad1cb0ae0ed48776ad870a7b1e61cdd08d80fb4a787d59 xsa396-linux-12.patch $ CREDITS ======= This issue was discovered by Demi Marie Obenour and Simon Gaiser of Invisible Things Lab. DEPLOYMENT DURING EMBARGO ========================= Deployment of patches or mitigations is NOT permitted (except where all the affected VMs are administered and used only by organisations which are members of the Xen Project Security Issues Predisclosure List). Specifically, deployment on public cloud systems is NOT permitted. This is because the patches need to be applied in the affected guests. Switching from PV to non-PV devices is observable by the guests and has usually a bad performance impact. Deployment is permitted only AFTER the embargo ends. (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/4UyVfoK9kFAmIp2PYMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZKEAIAKS8IFrluU7bw2k0ll8LfDdwI1skWPzEW++bsEjl G3eS2bIzOsI/HO5j8HKkxu7N/bPZF8U82+yrDtBYk7y1E8YnqoSyUB4Lc3Bv71gQ 6MVaLasbY5GrfUdK5lZyoepjudiPa+1/dOO7W3ZOJm7eLq0dTnTuR7vkyqEKQ2vY tYC+ubssufuo1FevGANuh2XZe6GUY9hqpBpyVwqArbUVicKC1RhKfBDYyZpSXd/W BIzwTZdWQlRIvu4TyPQTdFRjGH4gVf8roquHXDTJUHtItxomltq7irGdw/89y7EM 8abL+ZlUYHCb03RCT6ccTmExyVDrJ3h1JmWrqnIXpvApyAU= =b5Zc -----END PGP SIGNATURE-----
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