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

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

libfs: set SBINOEXEC and SBINODEV by default in initpseudo()

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

WARNING: CPU: 11 PID: 121813 at fs/exec.c:118 pathnoexec+0x47/0x50 dommap+0x2b5/0x680 vmmmappgoff+0x129/0x210 ksysmmappgoff+0x177/0x240 x64sysmmap+0x33/0x70

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

SBINODEV is inert for unreachable mounts. SBINOEXEC 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 CONFIGDEBUGVFS=y:

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