CVE-2026-74641: ALSA: usx2y: bound the hwdep mmap fault offset

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

ALSA: usx2y: bound the hwdep mmap fault offset

sndus428ctlsvmfault() turns the faulting page offset into a kernel address with no bound of any kind:

offset = vmf->pgoff << PAGESHIFT; vaddr = (char )(...)->us428ctlssharedmem + offset; page = virttopage(vaddr); getpage(page); vmf->page = page;

return 0;

sndus428ctlsmmap() checks only the length of the mapping, never the offset, and us428ctlssharedmem is a single page from allocpagesexact(). For a character device filemmapsizemax() returns ULONGMAX, so the mm layer imposes no ceiling either. Every page offset above zero resolves to a struct page outside the object, and the handler installs it into the caller's address space read-write; the vma is not marked read-only.

The caller picks the page frame with a single mmap() argument and gets read-write access to a page of kernel memory it does not own; an offset that lands in an unpopulated vmemmap region oopses instead.

A process that can open the hwdep node of an attached US-X2Y reaches this after loading the FPGA image through the same node; no capability check is involved.

On 7.2.0-rc5 (arm64), mmap() with a large offset:

Unable to handle kernel paging request at virtual address fffffdffc45d5ac8 pc : sndus428ctlsvmfault+0x68/0x140 [sndusbusx2y] Call trace: sndus428ctlsvmfault+0x68/0x140 [sndusbusx2y] dofault handlemmfault handlemmfault el0da

Reject any offset outside the shared region. The pcm hwdep handler in usx2yhwdeppcm.c computes its address the same way and needs the same bound.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>