Bug 2461507 (CVE-2026-31602)

Summary:	CVE-2026-31602 kernel: ALSA: ctxfi: Limit PTP to a single page
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	unspecified	CC:	rhel-process-autobot, 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 ALSA (Advanced Linux Sound Architecture) `ctxfi` driver. When handling memory allocations, the `ct_vm_map()` function can attempt to access memory beyond its allocated boundaries if aggregate memory allocations exceed a single page limit. This out-of-bounds access triggers a page fault, which can lead to a system crash. A local attacker could exploit this vulnerability to cause a Denial of Service (DoS) on the affected system.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-04-24 15:05:35 UTC

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

ALSA: ctxfi: Limit PTP to a single page

Commit 391e69143d0a increased CT_PTP_NUM from 1 to 4 to support 256
playback streams, but the additional pages are not used by the card
correctly. The CT20K2 hardware already has multiple VMEM_PTPAL
registers, but using them separately would require refactoring the
entire virtual memory allocation logic.

ct_vm_map() always uses PTEs in vm->ptp[0].area regardless of
CT_PTP_NUM. On AMD64 systems, a single PTP covers 512 PTEs (2M). When
aggregate memory allocations exceed this limit, ct_vm_map() tries to
access beyond the allocated space and causes a page fault:

  BUG: unable to handle page fault for address: ffffd4ae8a10a000
  Oops: Oops: 0002 [#1] SMP PTI
  RIP: 0010:ct_vm_map+0x17c/0x280 [snd_ctxfi]
  Call Trace:
  atc_pcm_playback_prepare+0x225/0x3b0
  ct_pcm_playback_prepare+0x38/0x60
  snd_pcm_do_prepare+0x2f/0x50
  snd_pcm_action_single+0x36/0x90
  snd_pcm_action_nonatomic+0xbf/0xd0
  snd_pcm_ioctl+0x28/0x40
  __x64_sys_ioctl+0x97/0xe0
  do_syscall_64+0x81/0x610
  entry_SYSCALL_64_after_hwframe+0x76/0x7e

Revert CT_PTP_NUM to 1. The 256 SRC_RESOURCE_NUM and playback_count
remain unchanged.

Comment 1 Keith Grant 2026-04-24 19:25:03 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042419-CVE-2026-31602-39fc@gregkh/T