Bug 1945663 (CVE-2021-28688) - CVE-2021-28688 xen: Linux blkback driver may leak persistent grants (XSA 371)
Summary: CVE-2021-28688 xen: Linux blkback driver may leak persistent grants (XSA 371)
Alias: CVE-2021-28688
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1945664
Blocks: 1940457
TreeView+ depends on / blocked
Reported: 2021-04-01 15:07 UTC by Michael Kaplan
Modified: 2021-04-05 21:24 UTC (History)
3 users (show)

Fixed In Version:
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Clone Of:
Last Closed: 2021-04-01 17:35:10 UTC

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Description Michael Kaplan 2021-04-01 15:07:48 UTC
The fix for XSA-365 includes initialization of pointers such that
subsequent cleanup code wouldn't use uninitialized or stale values.
This initialization went too far and may under certain conditions also
overwrite pointers which are in need of cleaning up.  The lack of
cleanup would result in leaking persistent grants.  The leak in turn
would prevent fully cleaning up after a respective guest has died,
leaving around zombie domains.


A malicious or buggy frontend driver may be able to cause resource leaks
from the corresponding backend driver.  This can result in a host-wide
Denial of Sevice (DoS).


Reconfiguring guests to use alternative (e.g. qemu-based) backends may
avoid the vulnerability.

Avoiding the use of persistent grants will also avoid the vulnerability.
This can be achieved by passing the "feature_persistent=0" module option
to the xen-blkback driver.

Comment 1 Michael Kaplan 2021-04-01 15:08:02 UTC
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1945664]

Comment 2 Product Security DevOps Team 2021-04-01 17:35:10 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.

Comment 3 Justin M. Forbes 2021-04-05 21:24:35 UTC
This was fixed for Fedora with the 5.11.11 stable kernel updates.

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