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xenXen ProjectXSA-361
HistoryFeb 16, 2021 - 12:00 p.m.

Linux: grant mapping error handling issues

2021-02-1612:00:00
Xen Project
xenbits.xen.org
44

5.5 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

1.9 Low

CVSS2

Access Vector

LOCAL

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

PARTIAL

AV:L/AC:M/Au:N/C:N/I:N/A:P

0.0004 Low

EPSS

Percentile

12.6%

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.

5.5 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

1.9 Low

CVSS2

Access Vector

LOCAL

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

PARTIAL

AV:L/AC:M/Au:N/C:N/I:N/A:P

0.0004 Low

EPSS

Percentile

12.6%

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