Bug 1903126 (CVE-2020-28974) - CVE-2020-28974 kernel: slab-out-of-bounds read in fbcon
Summary: CVE-2020-28974 kernel: slab-out-of-bounds read in fbcon
Keywords:
Status: CLOSED ERRATA
Alias: CVE-2020-28974
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard:
Depends On: 1903128 1903934 1903935 1903936 1903937 1903938 1940053
Blocks: 1895876
TreeView+ depends on / blocked
 
Reported: 2020-12-01 12:03 UTC by msiddiqu
Modified: 2024-03-25 17:18 UTC (History)
53 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
An out-of-bounds (OOB) SLAB memory access flaw was found in the Linux kernel's fbcon driver module. A bounds check failure allows a local attacker with special user privileges to gain access to out-of-bounds memory, leading to a system crash or leaking of internal kernel information. The highest threat from this vulnerability is to system availability.
Clone Of:
Environment:
Last Closed: 2021-05-18 20:37:41 UTC
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2021:2538 0 None None None 2021-06-23 18:06:20 UTC
Red Hat Product Errata RHBA-2021:2541 0 None None None 2021-06-24 11:51:40 UTC

Description msiddiqu 2020-12-01 12:03:24 UTC 
An out-of-bounds (OOB) SLAB memory access flaw was found in the fbcon driver module in the Linux kernel. A bounds check failure allows a local attacker with special user privilege to gain access to out-of-bounds memory leading to a system crash or a leak of internal kernel information. The highest threat from this vulnerability is to system availability.

This occurs because KD_FONT_OP_COPY in drivers/tty/vt/vt.c can be used for manipulations such as font height.

References: 
 
http://www.openwall.com/lists/oss-security/2020/11/25/1
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.9.7
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3c4e0dff2095c579b142d5a0693257f1c58b4804
https://seclists.org/oss-sec/2020/q4/104
Comment 1 msiddiqu 2020-12-01 12:04:30 UTC 
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1903128]
Comment 2 Justin M. Forbes 2020-12-01 13:49:19 UTC 
This was fixed for Fedora with the 5.9.7 stable kernel updates.
Comment 6 Rohit Keshri 2020-12-03 09:40:33 UTC 
Acknowledgments:

Name: Yuan Ming <yuanmingbuaa@gmail com> (Tsinghua University)
Comment 13 Rohit Keshri 2021-03-25 17:54:22 UTC 
Mitigation:

Add 'nomodeset' option as kernel boot parameter to disable frame buffering in /etc/default/grub, and run 'grub2-mkconfig -o /boot/grub2/grub.cfg' and reboot.
~~~
# cat /proc/cmdline 
BOOT_IMAGE=(hd0,msdos1)/vmlinuz-4.18.0-147.el8.x86_64 root=/dev/mapper/rhel_rhel8u2--1-root ro crashkernel=auto resume=/dev/mapper/rhel_rhel8u2--1-swap rd.lvm.lv=rhel_rhel8u2-1/root rd.lvm.lv=rhel_rhel8u2-1/swap nomodeset

# ls -l /dev/fb*
ls: cannot access '/dev/fb*': No such file or directory
~~~

The above said mitigation does not so effect for rhel6 kernel , and is only applicable for rhel7/8.
Comment 14 Steve Barcomb 2021-04-09 01:09:50 UTC 
*** Bug 1903934 has been marked as a duplicate of this bug. ***
Comment 15 errata-xmlrpc 2021-05-18 13:20:48 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:1578 https://access.redhat.com/errata/RHSA-2021:1578
Comment 16 errata-xmlrpc 2021-05-18 14:41:07 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:1739 https://access.redhat.com/errata/RHSA-2021:1739
Comment 17 Product Security DevOps Team 2021-05-18 20:37:41 UTC 
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2020-28974
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