Bug 2031194 (CVE-2021-4095)

Summary:	CVE-2021-4095 kernel: KVM: NULL pointer dereference in kvm_dirty_ring_get() in virt/kvm/dirty_ring.c
Product:	[Other] Security Response	Reporter:	Guilherme de Almeida Suckevicz <gsuckevi>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	acaringi, adscvr, airlied, alciregi, bhu, blc, brdeoliv, bskeggs, carnil, chwhite, crwood, dhoward, dvlasenk, fhrbata, fpacheco, hdegoede, hkrzesin, jarod, jarodwilson, jburrell, jeremy, jfaracco, jforbes, jglisse, jlelli, jonathan, josef, jshortt, jstancek, jwboyer, kcarcia, kernel-maint, kernel-mgr, lgoncalv, linville, lzampier, masami256, mchehab, mlangsdo, nmurray, ptalbert, qzhao, rvrbovsk, scweaver, steved, vkumar, walters, williams
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	kernel 5.17	Doc Type:	If docs needed, set a value
Doc Text:	A NULL pointer dereference was found in the Linux kernel's KVM when dirty ring logging is enabled without an active vCPU context. An unprivileged local attacker on the host may use this flaw to cause a kernel oops condition and thus a denial of service by issuing a KVM_XEN_HVM_SET_ATTR ioctl.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-12-16 15:15:09 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:	2031195
Bug Blocks:	2026458, 2031196

Description Guilherme de Almeida Suckevicz 2021-12-10 18:20:34 UTC

A NULL pointer dereference in kvm_dirty_ring_get() in virt/kvm/dirty_ring.c via a KVM KVM_XEN_HVM_SET_ATTR ioctl when there is no vCPU created.

References:
https://lore.kernel.org/kvm/CAFcO6XOmoS7EacN_n6v4Txk7xL7iqRa2gABg3F7E3Naf5uG94g@mail.gmail.com/
https://patchwork.kernel.org/project/kvm/patch/20211121125451.9489-12-dwmw2@infradead.org/

Comment 1 Guilherme de Almeida Suckevicz 2021-12-10 18:21:26 UTC

Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 2031195]

Comment 4 Mauro Matteo Cascella 2022-01-17 11:31:24 UTC

The patch for this issue is now available upstream:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=55749769fe608fa3f4a075e42e89d237c8e37637