---===[ Qubes Security Bulletin 064 ]===---

                             2021-02-16


   Linux: error handling issues in blkback's grant mapping (XSA-365)


User action required
=====================

Users must install the following specific packages in order to address
the issues discussed in this bulletin:

  For Qubes 4.0:
  - Linux kernel packages, versions 5.10.16-1, 5.4.98-1, 4.19.176-1

  For Qubes 4.1:
  - Linux kernel packages, versions 5.10.16-1, 5.4.98-1

The packages are to be installed in dom0 via the Qube Manager or via
the qubes-dom0-update command as follows:

  For updates from the stable repository (not immediately available):
  $ sudo qubes-dom0-update

  For updates from the security-testing repository:
  $ sudo qubes-dom0-update --enablerepo=qubes-dom0-security-testing

A system restart will be required afterwards.

These packages will migrate from the security-testing repository to the
current (stable) repository over the next two weeks after being tested
by the community.

If you use Anti Evil Maid, you will need to reseal your secret
passphrase to new PCR values, as PCR18+19 will change due to the new
Linux kernel binaries.


Summary
========

On 2021-02-16, the Xen Security Team published the following Xen
Security Advisory (XSA):

XSA-365 [1] "Linux: error handling issues in blkback's grant mapping"
| To service requests, the driver maps grant references provided by the
| frontend.  In this process, errors may be encountered.  In one case an
| error encountered earlier might be discarded by later processing,
| resulting in the caller assuming successful mapping, and hence
| subsequent operations trying to access space that wasn't mapped.  In
| another case internal state would be insufficiently updated, preventing
| safe recovery from the error.


Impact
=======

XSA-365, as described by Xen Security Team:
| A malicious or buggy frontend driver may be able to crash the
| corresponding backend driver, potentially affecting the entire domain
| running the backend driver.  In configurations without driver domains
| or similar disaggregation, that is a host-wide denial of sevice.
| 
| Privilege escalation and information leaks cannot be ruled out.


Credits
========

See the original Xen Security Advisories.


References
===========

[1] https://xenbits.xen.org/xsa/advisory-365.html

--
The Qubes Security Team
https://www.qubes-os.org/security/