Bug 1784923 (CVE-2019-19816)

Summary:	CVE-2019-19816 kernel: out-of-bounds write in __btrfs_map_block in fs/btrfs/volumes.c
Product:	[Other] Security Response	Reporter:	Guilherme de Almeida Suckevicz <gsuckevi>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED WONTFIX	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	acaringi, airlied, bdettelb, bhu, blc, brdeoliv, bskeggs, cmaiolin, dhoward, dvlasenk, esammons, fhrbata, hdegoede, hkrzesin, iboverma, ichavero, itamar, jarodwilson, jeremy, jforbes, jglisse, jlelli, john.j5live, jonathan, josef, jross, jschorr, jshortt, jstancek, jwboyer, kernel-maint, kernel-mgr, labbott, lgoncalv, linville, masami256, matt, mchehab, mcressma, mjg59, mlangsdo, nmurray, qzhao, rt-maint, rvrbovsk, steved, williams, wmealing
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in the implementation of the BTRFS file system code in the Linux kernel. An attacker, who is able to mount a crafted BTRFS filesystem and perform common filesystem operations, can possibly cause an out-of-bounds write to memory. This could lead to memory corruption or privilege escalation.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2020-04-01 09:04:21 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:	1784925, 1819509, 1819510, 1819511, 1819512, 1819513
Bug Blocks:	1784924

Description Guilherme de Almeida Suckevicz 2019-12-18 17:58:57 UTC

A flaw was found in the implementation of the BTRFS file system code.  An attacker who is able to mount (or convince someone to mount) a crafted BTRFS filesystem and performing common filesystem operations can possibly cause an out-of-bounds write to memory.

This could lead to memory corruption or possibly privilege escalation.  

Reference:
https://github.com/bobfuzzer/CVE/tree/master/CVE-2019-19816

Comment 1 Guilherme de Almeida Suckevicz 2019-12-18 17:59:55 UTC

Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1784925]

Comment 8 Eric Christensen 2020-04-01 15:53:10 UTC

Mitigation:

As the BTRFS module will be auto-loaded when required, its use can be disabled by preventing the module from loading with the following instructions:

# echo "install btrfs /bin/true" >> /etc/modprobe.d/disable-btrfs.conf

The system will need to be restarted if the BTRFS modules are loaded, it may be possible to unload them. In most circumstances, the BTRFS kernel modules will be unable to be unloaded while any BTRFS filesystems are mounted or in use.

If the system requires this module to work correctly, this mitigation may not be suitable.

If you need further assistance, see KCS article https://access.redhat.com/solutions/41278 or contact Red Hat Global Support Services.

Comment 9 Petr Matousek 2020-04-03 04:42:44 UTC

Statement:

This flaw is rated as having Moderate impact, the attacker would require physical access to the system and also a local account to abuse the use-after-free.

Comment 10 Justin M. Forbes 2020-06-26 17:14:47 UTC

This was fixed for Fedora with the 5.2 kernel rebases.