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

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

ALSA: usx2y: bound the hwdep mmap fault offset

snd_us428ctls_vm_fault() turns the faulting page offset into a kernel
address with no bound of any kind:

	offset = vmf->pgoff << PAGE_SHIFT;
	vaddr = (char *)(...)->us428ctls_sharedmem + offset;
	page = virt_to_page(vaddr);
	get_page(page);
	vmf->page = page;

	return 0;

snd_us428ctls_mmap() checks only the length of the mapping, never the
offset, and us428ctls_sharedmem is a single page from
alloc_pages_exact().  For a character device file_mmap_size_max()
returns ULONG_MAX, 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 : snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y]
  Call trace:
   snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y]
   __do_fault
   __handle_mm_fault
   handle_mm_fault
   el0_da

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 <[email protected]>

The Linux kernel CVE team has assigned CVE-2026-74641 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.15.216 with commit 10a87401fb3148c388e55df0148295b3b137da07
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.183 with commit 34ab56ed854baa73a731cfd99af689f0b1bac444
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.152 with commit 4208db2453e1ea71b8048a5b7802360cb29a53f1
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.104 with commit f613b4a2d87247b51a1b2b330f2e083a454125f2
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.45 with commit f75d6f61f0d9c5c1ea725104014e10d26d1e3a00
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.1.9 with commit 5bf5ccddf00b59f1e3ea7e65d76a5f5b5c21cc2e
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2 with commit 2ca1eea3cd17930daffe9e429a7c89232036ec24

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74641
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	sound/usb/usx2y/usX2Yhwdep.c
	sound/usb/usx2y/usx2yhwdeppcm.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/10a87401fb3148c388e55df0148295b3b137da07
	https://git.kernel.org/stable/c/34ab56ed854baa73a731cfd99af689f0b1bac444
	https://git.kernel.org/stable/c/4208db2453e1ea71b8048a5b7802360cb29a53f1
	https://git.kernel.org/stable/c/f613b4a2d87247b51a1b2b330f2e083a454125f2
	https://git.kernel.org/stable/c/f75d6f61f0d9c5c1ea725104014e10d26d1e3a00
	https://git.kernel.org/stable/c/5bf5ccddf00b59f1e3ea7e65d76a5f5b5c21cc2e
	https://git.kernel.org/stable/c/2ca1eea3cd17930daffe9e429a7c89232036ec24