Bug 1272472 (CVE-2015-7837)

Summary: CVE-2015-7837 kernel: securelevel disabled after kexec
Product: [Other] Security Response Reporter: Adam Mariš <amaris>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: aquini, bhu, dhoward, fhrbata, iboverma, jbastian, jkacur, joelsmith, jross, kernel-mgr, kstutsma, lgoncalv, matt, mcressma, mrg-program-list, nmurray, osoukup, plougher, pmatouse, rvrbovsk, slawomir, vdronov, williams, wmealing
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
A flaw was found in the way the Linux kernel handled the securelevel functionality after performing a kexec operation. A local attacker could use this flaw to bypass the security mechanism of the securelevel/secureboot combination.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2019-06-08 02:44:12 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 1243998, 1273216, 1273217, 1273218, 1273219, 1273220, 1273221    
Bug Blocks: 1247887    

Description Adam Mariš 2015-10-16 13:25:20 UTC 
A vulnerability was found in kexec, allowing the attacker to bypass the security mechanism of securelevel/secureboot combination.

When the kernel was booted with UEFI Secure Boot enabled, securelevel is set. If kexec (either through crash or admin action) is then used to load the same kernel, after reboot securelevel is disabled. In this state, the system is missing the protections provided by securelevel, for example kexec may be used to load an unsigned kernel via the legacy system call kexec_load. In the securelevel patchset, the state of UEFI Secure Boot is queried in the EFI stub, and sets a boot_params flag to indicate the state of UEFI Secure Boot. This flag is then used in setup_arch() to determine the correct state of securelevel. If the kernel is not booted via the EFI stub, securelevel is not set even if UEFI Secure Boot is enabled.

Patch can be found in product bug:

https://bugzilla.redhat.com/show_bug.cgi?id=1243998#c3

Upstream patch:

https://github.com/mjg59/linux/commit/4b2b64d5a6ebc84214755ebccd599baef7c1b798

CVE assignment:

http://seclists.org/oss-sec/2015/q4/85
Comment 3 Wade Mealing 2015-10-20 03:38:50 UTC 
Statement:

This issue does not affect the Linux kernels as shipped with Red Hat Enterprise Linux 5 and 6.

This issue affects the Linux kernels as shipped with Red Hat Enterprise Linux 7, kernel-rt and MRG-2.
Comment 6 errata-xmlrpc 2015-11-19 13:22:17 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2015:2411 https://rhn.redhat.com/errata/RHSA-2015-2411.html
Comment 7 errata-xmlrpc 2015-11-19 23:22:20 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2015:2152 https://rhn.redhat.com/errata/RHSA-2015-2152.html
Comment 8 errata-xmlrpc 2015-11-19 23:27:17 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2015:2152 https://rhn.redhat.com/errata/RHSA-2015-2152.html