On Mon, Mar 16, 2026 at 10:53 PM Jeff Layton [off-list ref] wrote:

On Sat, 2026-03-07 at 20:06 +0600, Dorjoy Chowdhury wrote:

quoted

This flag indicates the path should be opened if it's a regular file.
This is useful to write secure programs that want to avoid being
tricked into opening device nodes with special semantics while thinking
they operate on regular files. This is a requested feature from the
uapi-group[1].

A corresponding error code EFTYPE has been introduced. For example, if
openat2 is called on path /dev/null with OPENAT2_REGULAR in the flag
param, it will return -EFTYPE. EFTYPE is already used in BSD systems
like FreeBSD, macOS.

When used in combination with O_CREAT, either the regular file is
created, or if the path already exists, it is opened if it's a regular
file. Otherwise, -EFTYPE is returned.

When OPENAT2_REGULAR is combined with O_DIRECTORY, -EINVAL is returned
as it doesn't make sense to open a path that is both a directory and a
regular file.

[1]: https://uapi-group.org/kernel-features/#ability-to-only-open-regular-files

Signed-off-by: Dorjoy Chowdhury <redacted>
---
 arch/alpha/include/uapi/asm/errno.h        |  2 ++
 arch/alpha/include/uapi/asm/fcntl.h        |  1 +
 arch/mips/include/uapi/asm/errno.h         |  2 ++
 arch/parisc/include/uapi/asm/errno.h       |  2 ++
 arch/parisc/include/uapi/asm/fcntl.h       |  1 +
 arch/sparc/include/uapi/asm/errno.h        |  2 ++
 arch/sparc/include/uapi/asm/fcntl.h        |  1 +
 fs/ceph/file.c                             |  4 ++++
 fs/gfs2/inode.c                            |  6 ++++++
 fs/namei.c                                 |  4 ++++
 fs/nfs/dir.c                               |  4 ++++
 fs/open.c                                  |  4 +++-
 fs/smb/client/dir.c                        | 14 +++++++++++++-
 include/linux/fcntl.h                      |  2 ++
 include/uapi/asm-generic/errno.h           |  2 ++
 include/uapi/asm-generic/fcntl.h           |  4 ++++
 tools/arch/alpha/include/uapi/asm/errno.h  |  2 ++
 tools/arch/mips/include/uapi/asm/errno.h   |  2 ++
 tools/arch/parisc/include/uapi/asm/errno.h |  2 ++
 tools/arch/sparc/include/uapi/asm/errno.h  |  2 ++
 tools/include/uapi/asm-generic/errno.h     |  2 ++
 21 files changed, 63 insertions(+), 2 deletions(-)

I pointed Claude at this patch and got this back. Both issues that it
found will need to be fixed:

  Analysis Summary

  Commit: 7e7fa2653ca57 - openat2: new OPENAT2_REGULAR flag support

  This patch adds a new OPENAT2_REGULAR flag for openat2() that restricts opens to regular files only, returning a new
  EFTYPE errno for non-regular files. It adds filesystem-specific checks in ceph, gfs2, nfs, and cifs atomic_open paths,
  plus a VFS-level fallback in do_open().

  Issues found:

  1. OPENAT2_REGULAR leaks into f_flags - do_dentry_open() strips open-time-only flags (O_CREAT|O_EXCL|O_NOCTTY|O_TRUNC)
  but does not strip OPENAT2_REGULAR. When a regular file is successfully opened via openat2() with this flag, the bit
  persists in file->f_flags and will be returned by fcntl(fd, F_GETFL).
  2. BUILD_BUG_ON not updated - The compile-time guard checks upper_32_bits(VALID_OPEN_FLAGS) but the code now accepts
  VALID_OPENAT2_FLAGS. The guard should cover the expanded flag set.

Good catches! I guess for issue 1 I need to modify the line in
do_dentry_open implementation to
f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | OPENAT2_REGULAR);
right?
And for issue 2, I should change the VALID_OPEN_FLAGS to
VALID_OPENAT2_FLAGS in both build_open_flags in fs/open.c and in
fcntl_init in fs/fcntl.c, correct?

Regards,
Dorjoy