Bug 2002785 (CVE-2021-28701)

Summary: CVE-2021-28701 xen: another race in XENMAPSPACE_grant_table handling
Product: [Other] Security Response Reporter: Guilherme de Almeida Suckevicz <gsuckevi>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED UPSTREAM QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: jforbes, m.a.young
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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Last Closed: 2021-09-09 18:21:15 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2002786    
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Description Guilherme de Almeida Suckevicz 2021-09-09 17:59:56 UTC 
Another race in XENMAPSPACE_grant_table handling Guests are permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, are de-allocated when a guest switches (back) from v2 to v1. Freeing such pages requires that the hypervisor enforce that no parallel request can result in the addition of a mapping of such a page to a guest. That enforcement was missing, allowing guests to retain access to pages that were freed and perhaps re-used for other purposes. Unfortunately, when XSA-379 was being prepared, this similar issue was not noticed.

References:
https://xenbits.xenproject.org/xsa/advisory-384.txt
http://www.openwall.com/lists/oss-security/2021/09/08/2
Comment 1 Guilherme de Almeida Suckevicz 2021-09-09 18:00:12 UTC 
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 2002786]
Comment 2 Product Security DevOps Team 2021-09-09 18:21:15 UTC 
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.