Bug 2536394 (CVE-2026-93186)

Summary:	CVE-2026-93186 kernel: cxl/mbox: Clamp mailbox output allocation to the payload size
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's Compute Express Link (CXL) mailbox driver. A local attacker could exploit an unbounded memory allocation vulnerability in the `CXL_MEM_SEND_COMMAND` function. By providing a large output size, an attacker could trigger a huge memory allocation, potentially leading to a system panic and a denial of service.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
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Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-17 17:42:50 UTC

In the Linux kernel, the following vulnerability has been resolved:

cxl/mbox: Clamp mailbox output allocation to the payload size

CXL_MEM_SEND_COMMAND bounds the user's in.size to the mailbox payload
size but leaves out.size unbounded, then cxl_mbox_cmd_ctor() calls
kvzalloc(out.size). A large out.size drives a huge allocation, above
INT_MAX it WARNs and taints, and with panic_on_warn=1 it panics.

The transport __cxl_pci_mbox_send_cmd() already clamps the response copy
to min(out.size, payload_size, device len), so the output buffer is
never written beyond payload_size. Clamp the allocation to payload_size
too, matching the RAW path.

Comment 1 gkamathe 2026-09-18 07:34:29 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93186.mbox