CVE-2026-31602

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

ALSA: ctxfi: Limit PTP to a single page

Commit 391e69143d0a increased CTPTPNUM 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.

ctvmmap() always uses PTEs in vm->ptp[0].area regardless of CTPTPNUM. On AMD64 systems, a single PTP covers 512 PTEs (2M). When aggregate memory allocations exceed this limit, ctvmmap() 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:ctvmmap+0x17c/0x280 [sndctxfi] Call Trace: atcpcmplaybackprepare+0x225/0x3b0 ctpcmplaybackprepare+0x38/0x60 sndpcmdoprepare+0x2f/0x50 sndpcmactionsingle+0x36/0x90 sndpcmactionnonatomic+0xbf/0xd0 sndpcmioctl+0x28/0x40 __x64sysioctl+0x97/0xe0 dosyscall64+0x81/0x610 entrySYSCALL64afterhwframe+0x76/0x7e

Revert CTPTPNUM to 1. The 256 SRCRESOURCENUM and playback_count remain unchanged.