CVE-2026-64596: libfs: set SB_I_NOEXEC and SB_I_NODEV by default in init_pseudo()

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

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

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

libfs: set SB_I_NOEXEC and SB_I_NODEV by default in init_pseudo()

Since commit 1e7ab6f67824 ("anon_inode: rework assertions"),
path_noexec() warns when an anonymous-inode file is mmap'd from a
superblock that has not set SB_I_NOEXEC. dma-buf backs its files this
way and never set the flag, so mmap of any exported buffer trips the
warning on a CONFIG_DEBUG_VFS=y kernel:

  WARNING: CPU: 11 PID: 121813 at fs/exec.c:118 path_noexec+0x47/0x50
   do_mmap+0x2b5/0x680
   vm_mmap_pgoff+0x129/0x210
   ksys_mmap_pgoff+0x177/0x240
   __x64_sys_mmap+0x33/0x70

init_pseudo() sets up internal SB_NOUSER mounts that are never
path-reachable. Set both flags here so every pseudo filesystem gets
them by default instead of each caller setting them.

SB_I_NODEV is inert for unreachable mounts. SB_I_NOEXEC has one
visible effect: an executable mapping of a pseudo-fs fd, such as a
dma-buf, now fails with -EPERM, which is the invariant the assertion
enforces. No in-tree caller maps these executable.

Reproduce on CONFIG_DEBUG_VFS=y:

  make -C tools/testing/selftests/dmabuf-heaps
  sudo ./tools/testing/selftests/dmabuf-heaps/dmabuf-heap -t system

The Linux kernel CVE team has assigned CVE-2026-64596 to this issue.


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

	Issue introduced in 6.16 with commit 1e7ab6f67824343ee3e96f100f0937c393749a8a and fixed in 6.18.39 with commit b9d45d328fcda4f0d3d281b7d6f12d3f181d9381
	Issue introduced in 6.16 with commit 1e7ab6f67824343ee3e96f100f0937c393749a8a and fixed in 7.1.4 with commit 8e931557b317f0fb414839fa51fae1d5feb0ad97
	Issue introduced in 6.16 with commit 1e7ab6f67824343ee3e96f100f0937c393749a8a and fixed in 7.2-rc1 with commit 6de2aeffabaafaeda819e60ec8d04f199711e11a
	Issue introduced in 6.15.6 with commit 9b8076a9404568d6cb6673b9a079558b15051966

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-2026-64596
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:
	fs/libfs.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/b9d45d328fcda4f0d3d281b7d6f12d3f181d9381
	https://git.kernel.org/stable/c/8e931557b317f0fb414839fa51fae1d5feb0ad97
	https://git.kernel.org/stable/c/6de2aeffabaafaeda819e60ec8d04f199711e11a