CVE-2026-80633: iommufd: Take dma_resv lock before dma_buf_unpin() in release path

CVE-2026-80633: iommufd: Take dma_resv lock before dma_buf_unpin() in release path

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

iommufd: Take dma_resv lock before dma_buf_unpin() in release path

dma_buf_unpin() requires the caller to hold the exporter's dma_resv
lock:

  void dma_buf_unpin(struct dma_buf_attachment *attach)
  {
          ...
          dma_resv_assert_held(dmabuf->resv);
          ...
  }

iopt_release_pages() calls dma_buf_unpin() without taking that lock,
so every iommufd_ioas_destroy()/iommufd_ioas_unmap() that releases
the last reference on a DMABUF-backed iopt_pages triggers a WARN.
This was hit while running tools/testing/selftests/iommu/iommufd:

  WARNING: drivers/dma-buf/dma-buf.c:1137 at dma_buf_unpin+0x62/0x70
  RIP: 0010:dma_buf_unpin+0x62/0x70
  Call Trace:
   <TASK>
   dma_buf_unpin+0x62/0x70
   iopt_release_pages+0xe4/0x190
   iopt_unmap_iova_range+0x1c7/0x290
   iopt_unmap_all+0x1a/0x30
   iommufd_ioas_destroy+0x1d/0x50
   iommufd_fops_release+0x93/0x150
   __fput+0xfc/0x2c0
   __x64_sys_close+0x3d/0x80
   do_syscall_64+0x65/0x180
   </TASK>

Take the dma_resv lock around dma_buf_unpin() in iopt_release_pages(),
matching the iopt_map_dmabuf() convention. dma_buf_detach() acquires the
reservation lock internally, so it must remain outside the locked region.

The Linux kernel CVE team has assigned CVE-2026-80633 to this issue.


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

	Issue introduced in 7.1 with commit 8c5f9645c3893f0db679d9affe4fe4e665b990dd and fixed in 7.1.5 with commit cc69d0332421fd2943b66dbe5e597bf4fd5af126
	Issue introduced in 7.1 with commit 8c5f9645c3893f0db679d9affe4fe4e665b990dd and fixed in 7.2 with commit e745cd2c749e557c14a15ac931761c3f58c24489

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-2026-80633
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:
	drivers/iommu/iommufd/pages.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/cc69d0332421fd2943b66dbe5e597bf4fd5af126
	https://git.kernel.org/stable/c/e745cd2c749e557c14a15ac931761c3f58c24489