Re: [PATCH v4 1/4] openat2: new OPENAT2_REGULAR flag support

Jeff Layton
2026-03-01T12:44:44Z

On Sat, 2026-02-21 at 20:45 +0600, Dorjoy Chowdhury wrote:
> 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.
>
> 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.
>

It would be good to mention that EFTYPE has precedent in BSD/Darwin.
When an error code is already supported in another UNIX-y OS, then it
bolsters the case for adding it here.

Your cover letter mentions that you only tested this on btrfs. At the
very least, you should test NFS and SMB. It should be fairly easy to
set up mounts over loopback for those cases.

There are some places where it doesn't seem like -EFTYPE will be
returned. It looks like it can send back -EISDIR and -ENOTDIR in some
cases as well. With a new API like this, I think we ought to strive for
consistency.

Should this API return -EFTYPE for all cases where it's not S_IFREG? If
not, then what other errors are allowed? Bear in mind that you'll need
to document this in the manpages too.

> 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 <dorjoychy111@gmail.com>
> ---
> 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 | 2 ++
> fs/namei.c | 4 ++++
> fs/nfs/dir.c | 4 +++-
> fs/open.c | 4 +++-
> fs/smb/client/dir.c | 11 ++++++++++-
> 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, 55 insertions(+), 3 deletions(-)
>
> diff --git a/arch/alpha/include/uapi/asm/errno.h b/arch/alpha/include/uapi/asm/errno.h
> index 6791f6508632..1a99f38813c7 100644
> --- a/arch/alpha/include/uapi/asm/errno.h
> +++ b/arch/alpha/include/uapi/asm/errno.h
> @@ -127,4 +127,6 @@
>
> #define EHWPOISON 139 /* Memory page has hardware error */
>
> +#define EFTYPE 140 /* Wrong file type for the intended operation */
> +
> #endif
> diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h
> index 50bdc8e8a271..fe488bf7c18e 100644
> --- a/arch/alpha/include/uapi/asm/fcntl.h
> +++ b/arch/alpha/include/uapi/asm/fcntl.h
> @@ -34,6 +34,7 @@
>
> #define O_PATH 040000000
> #define __O_TMPFILE 0100000000
> +#define OPENAT2_REGULAR 0200000000
>
> #define F_GETLK 7
> #define F_SETLK 8
> diff --git a/arch/mips/include/uapi/asm/errno.h b/arch/mips/include/uapi/asm/errno.h
> index c01ed91b1ef4..1835a50b69ce 100644
> --- a/arch/mips/include/uapi/asm/errno.h
> +++ b/arch/mips/include/uapi/asm/errno.h
> @@ -126,6 +126,8 @@
>
> #define EHWPOISON 168 /* Memory page has hardware error */
>
> +#define EFTYPE 169 /* Wrong file type for the intended operation */
> +
> #define EDQUOT 1133 /* Quota exceeded */
>
>
> diff --git a/arch/parisc/include/uapi/asm/errno.h b/arch/parisc/include/uapi/asm/errno.h
> index 8cbc07c1903e..93194fbb0a80 100644
> --- a/arch/parisc/include/uapi/asm/errno.h
> +++ b/arch/parisc/include/uapi/asm/errno.h
> @@ -124,4 +124,6 @@
>
> #define EHWPOISON 257 /* Memory page has hardware error */
>
> +#define EFTYPE 258 /* Wrong file type for the intended operation */
> +
> #endif
> diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h
> index 03dee816cb13..d46812f2f0f4 100644
> --- a/arch/parisc/include/uapi/asm/fcntl.h
> +++ b/arch/parisc/include/uapi/asm/fcntl.h
> @@ -19,6 +19,7 @@
>
> #define O_PATH 020000000
> #define __O_TMPFILE 040000000
> +#define OPENAT2_REGULAR 0100000000
>
> #define F_GETLK64 8
> #define F_SETLK64 9
> diff --git a/arch/sparc/include/uapi/asm/errno.h b/arch/sparc/include/uapi/asm/errno.h
> index 4a41e7835fd5..71940ec9130b 100644
> --- a/arch/sparc/include/uapi/asm/errno.h
> +++ b/arch/sparc/include/uapi/asm/errno.h
> @@ -117,4 +117,6 @@
>
> #define EHWPOISON 135 /* Memory page has hardware error */
>
> +#define EFTYPE 136 /* Wrong file type for the intended operation */
> +
> #endif
> diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h
> index 67dae75e5274..bb6e9fa94bc9 100644
> --- a/arch/sparc/include/uapi/asm/fcntl.h
> +++ b/arch/sparc/include/uapi/asm/fcntl.h
> @@ -37,6 +37,7 @@
>
> #define O_PATH 0x1000000
> #define __O_TMPFILE 0x2000000
> +#define OPENAT2_REGULAR 0x4000000
>
> #define F_GETOWN 5 /* for sockets. */
> #define F_SETOWN 6 /* for sockets. */
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index 31b691b2aea2..0a4220f72ada 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -977,6 +977,10 @@ int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
> ceph_init_inode_acls(newino, &as_ctx);
> file->f_mode |= FMODE_CREATED;
> }
> + if ((flags & OPENAT2_REGULAR) && !d_is_reg(dentry)) {
> + err = -EFTYPE;
> + goto out_req;
> + }
> err = finish_open(file, dentry, ceph_open);
> }
> out_req:
> diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
> index 8344040ecaf7..0dc3e4240d9e 100644
> --- a/fs/gfs2/inode.c
> +++ b/fs/gfs2/inode.c
> @@ -749,6 +749,8 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
> if (file) {
> if (S_ISREG(inode->i_mode))
> error = finish_open(file, dentry, gfs2_open_common);
> + else if (file->f_flags & OPENAT2_REGULAR)
> + error = -EFTYPE;
> else
> error = finish_no_open(file, NULL);
> }
> diff --git a/fs/namei.c b/fs/namei.c
> index 5fe6cac48df8..aa5fb2672881 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4651,6 +4651,10 @@ static int do_open(struct nameidata *nd,
> if (unlikely(error))
> return error;
> }
> +
> + if ((open_flag & OPENAT2_REGULAR) && !d_is_reg(nd->path.dentry))
> + return -EFTYPE;
> +
> if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
> return -ENOTDIR;
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index b3f5c9461204..ef61db67d06e 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -2195,7 +2195,9 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
> break;
> case -EISDIR:
> case -ENOTDIR:
> - goto no_open;
> + if (!(open_flags & OPENAT2_REGULAR))
> + goto no_open;
> + break;

Shouldn't this also set the error to -EFTYPE?

> case -ELOOP:
> if (!(open_flags & O_NOFOLLOW))
> goto no_open;
> diff --git a/fs/open.c b/fs/open.c
> index 91f1139591ab..1524f52a1773 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -1198,7 +1198,7 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op)
> * values before calling build_open_flags(), but openat2(2) checks all
> * of its arguments.
> */
> - if (flags & ~VALID_OPEN_FLAGS)
> + if (flags & ~VALID_OPENAT2_FLAGS)
> return -EINVAL;
> if (how->resolve & ~VALID_RESOLVE_FLAGS)
> return -EINVAL;
> @@ -1237,6 +1237,8 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op)
> return -EINVAL;
> if (!(acc_mode & MAY_WRITE))
> return -EINVAL;
> + } else if ((flags & O_DIRECTORY) && (flags & OPENAT2_REGULAR)) {
> + return -EINVAL;
> }
> if (flags & O_PATH) {
> /* O_PATH only permits certain other flags to be set. */
> diff --git a/fs/smb/client/dir.c b/fs/smb/client/dir.c
> index cb10088197d2..d12ed0c87599 100644
> --- a/fs/smb/client/dir.c
> +++ b/fs/smb/client/dir.c
> @@ -236,6 +236,11 @@ static int cifs_do_create(struct inode *inode, struct dentry *direntry, unsigned
> * lookup.
> */
> CIFSSMBClose(xid, tcon, fid->netfid);
> + if (oflags & OPENAT2_REGULAR) {
> + iput(newinode);
> + rc = -EFTYPE;
> + goto out;
> + }
> goto cifs_create_get_file_info;
> }
> /* success, no need to query */
> @@ -433,11 +438,15 @@ static int cifs_do_create(struct inode *inode, struct dentry *direntry, unsigned
> goto out_err;
> }
>
> - if (newinode)
> + if (newinode) {
> if (S_ISDIR(newinode->i_mode)) {
> rc = -EISDIR;
> goto out_err;

This logic doesn't look quite right. If you do a create and race with a
directory create, then it looks like you'll send back -EISDIR here
instead of -EFTYPE?

> + } else if ((oflags & OPENAT2_REGULAR) && !S_ISREG(newinode->i_mode)) {
> + rc = -EFTYPE;
> + goto out_err;
> }
> + }
>
> d_drop(direntry);
> d_add(direntry, newinode);
> diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
> index a332e79b3207..a80026718217 100644
> --- a/include/linux/fcntl.h
> +++ b/include/linux/fcntl.h
> @@ -12,6 +12,8 @@
> FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \
> O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE)
>
> +#define VALID_OPENAT2_FLAGS (VALID_OPEN_FLAGS | OPENAT2_REGULAR)
> +
> /* List of all valid flags for the how->resolve argument: */
> #define VALID_RESOLVE_FLAGS \
> (RESOLVE_NO_XDEV | RESOLVE_NO_MAGICLINKS | RESOLVE_NO_SYMLINKS | \
> diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h
> index 92e7ae493ee3..bd78e69e0a43 100644
> --- a/include/uapi/asm-generic/errno.h
> +++ b/include/uapi/asm-generic/errno.h
> @@ -122,4 +122,6 @@
>
> #define EHWPOISON 133 /* Memory page has hardware error */
>
> +#define EFTYPE 134 /* Wrong file type for the intended operation */
> +
> #endif
> diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
> index 613475285643..b2c2ddd0edc0 100644
> --- a/include/uapi/asm-generic/fcntl.h
> +++ b/include/uapi/asm-generic/fcntl.h
> @@ -88,6 +88,10 @@
> #define __O_TMPFILE 020000000
> #endif
>
> +#ifndef OPENAT2_REGULAR
> +#define OPENAT2_REGULAR 040000000
> +#endif
> +
> /* a horrid kludge trying to make sure that this will fail on old kernels */
> #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
>
> diff --git a/tools/arch/alpha/include/uapi/asm/errno.h b/tools/arch/alpha/include/uapi/asm/errno.h
> index 6791f6508632..1a99f38813c7 100644
> --- a/tools/arch/alpha/include/uapi/asm/errno.h
> +++ b/tools/arch/alpha/include/uapi/asm/errno.h
> @@ -127,4 +127,6 @@
>
> #define EHWPOISON 139 /* Memory page has hardware error */
>
> +#define EFTYPE 140 /* Wrong file type for the intended operation */
> +
> #endif
> diff --git a/tools/arch/mips/include/uapi/asm/errno.h b/tools/arch/mips/include/uapi/asm/errno.h
> index c01ed91b1ef4..1835a50b69ce 100644
> --- a/tools/arch/mips/include/uapi/asm/errno.h
> +++ b/tools/arch/mips/include/uapi/asm/errno.h
> @@ -126,6 +126,8 @@
>
> #define EHWPOISON 168 /* Memory page has hardware error */
>
> +#define EFTYPE 169 /* Wrong file type for the intended operation */
> +
> #define EDQUOT 1133 /* Quota exceeded */
>
>
> diff --git a/tools/arch/parisc/include/uapi/asm/errno.h b/tools/arch/parisc/include/uapi/asm/errno.h
> index 8cbc07c1903e..93194fbb0a80 100644
> --- a/tools/arch/parisc/include/uapi/asm/errno.h
> +++ b/tools/arch/parisc/include/uapi/asm/errno.h
> @@ -124,4 +124,6 @@
>
> #define EHWPOISON 257 /* Memory page has hardware error */
>
> +#define EFTYPE 258 /* Wrong file type for the intended operation */
> +
> #endif
> diff --git a/tools/arch/sparc/include/uapi/asm/errno.h b/tools/arch/sparc/include/uapi/asm/errno.h
> index 4a41e7835fd5..71940ec9130b 100644
> --- a/tools/arch/sparc/include/uapi/asm/errno.h
> +++ b/tools/arch/sparc/include/uapi/asm/errno.h
> @@ -117,4 +117,6 @@
>
> #define EHWPOISON 135 /* Memory page has hardware error */
>
> +#define EFTYPE 136 /* Wrong file type for the intended operation */
> +
> #endif
> diff --git a/tools/include/uapi/asm-generic/errno.h b/tools/include/uapi/asm-generic/errno.h
> index 92e7ae493ee3..bd78e69e0a43 100644
> --- a/tools/include/uapi/asm-generic/errno.h
> +++ b/tools/include/uapi/asm-generic/errno.h
> @@ -122,4 +122,6 @@
>
> #define EHWPOISON 133 /* Memory page has hardware error */
>
> +#define EFTYPE 134 /* Wrong file type for the intended operation */
> +
> #endif

--
Jeff Layton <jlayton@kernel.org>