Re: [PATCH v6 1/4] openat2: new OPENAT2_REGULAR flag support

From: Dorjoy Chowdhury

Date: Sat Apr 04 2026 - 11:17:37 EST

On Thu, Apr 2, 2026 at 1:02 AM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> On Mon, 2026-03-30 at 21:07 +0600, Dorjoy Chowdhury wrote:
> > On Mon, Mar 30, 2026 at 5:49 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> > >
> > > On Sat, 2026-03-28 at 23:22 +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. 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 <dorjoychy111@xxxxxxxxx>
> > > > ---
> > > > 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/fcntl.c | 4 ++--
> > > > fs/gfs2/inode.c | 6 ++++++
> > > > fs/namei.c | 4 ++++
> > > > fs/nfs/dir.c | 4 ++++
> > > > fs/open.c | 8 +++++---
> > > > 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 ++
> > > > 22 files changed, 67 insertions(+), 6 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 66bbf6d517a9..6d8d4c7765e6 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;
> > > > + }
> > >
> > > ^^^
> > > This doesn't look quite right. Here's a larger chunk of the code:
> > >
> > > -------------------------8<--------------------------
> > > if (d_in_lookup(dentry)) {
> > > dn = ceph_finish_lookup(req, dentry, err);
> > > if (IS_ERR(dn))
> > > err = PTR_ERR(dn);
> > > } else {
> > > /* we were given a hashed negative dentry */
> > > dn = NULL;
> > > }
> > > if (err)
> > > goto out_req;
> > > if (dn || d_really_is_negative(dentry) || d_is_symlink(dentry)) {
> > > /* make vfs retry on splice, ENOENT, or symlink */
> > > doutc(cl, "finish_no_open on dn %p\n", dn);
> > > err = finish_no_open(file, dn);
> > > } else {
> > > if (IS_ENCRYPTED(dir) &&
> > > !fscrypt_has_permitted_context(dir, d_inode(dentry))) {
> > > pr_warn_client(cl,
> > > "Inconsistent encryption context (parent %llx:%llx child %llx:%llx)\n",
> > > ceph_vinop(dir), ceph_vinop(d_inode(dentry)));
> > > goto out_req;
> > > }
> > >
> > > doutc(cl, "finish_open on dn %p\n", dn);
> > > if (req->r_op == CEPH_MDS_OP_CREATE && req->r_reply_info.has_create_ino) {
> > > struct inode *newino = d_inode(dentry);
> > >
> > > cache_file_layout(dir, newino);
> > > ceph_init_inode_acls(newino, &as_ctx);
> > > file->f_mode |= FMODE_CREATED;
> > > }
> > > err = finish_open(file, dentry, ceph_open);
> > > }
> > > -------------------------8<--------------------------
> > >
> > > It looks like this won't handle it correctly if the pathwalk terminates
> > > on a symlink (re: d_is_symlink() case). You should either set up a test
> > > ceph cluster on your own, or reach out to the ceph community and ask
> > > them to test this.
> > >
> >
> > Thanks for reviewing. The d_is_symlink() case seems to be calling
> > finish_no_open so shouldn't this be okay?
> >
>
> My mistake -- you're correct. I keep forgetting that finish_no_open()
> will handle this case regardless of what else happens.
>
> > > > err = finish_open(file, dentry, ceph_open);
> > > > }
> > > > out_req:
> > > > diff --git a/fs/fcntl.c b/fs/fcntl.c
> > > > index beab8080badf..240bb511557a 100644
> > > > --- a/fs/fcntl.c
> > > > +++ b/fs/fcntl.c
> > > > @@ -1169,9 +1169,9 @@ static int __init fcntl_init(void)
> > > > * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
> > > > * is defined as O_NONBLOCK on some platforms and not on others.
> > > > */
> > > > - BUILD_BUG_ON(20 - 1 /* for O_RDONLY being 0 */ !=
> > > > + BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ !=
> > > > HWEIGHT32(
> > > > - (VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) |
> > > > + (VALID_OPENAT2_FLAGS & ~(O_NONBLOCK | O_NDELAY)) |
> > > > __FMODE_EXEC));
> > > >
> > > > fasync_cache = kmem_cache_create("fasync_cache",
> > > > diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
> > > > index 8344040ecaf7..4604e2e8a9cc 100644
> > > > --- a/fs/gfs2/inode.c
> > > > +++ b/fs/gfs2/inode.c
> > > > @@ -738,6 +738,12 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
> > > > inode = gfs2_dir_search(dir, &dentry->d_name, !S_ISREG(mode) || excl);
> > > > error = PTR_ERR(inode);
> > > > if (!IS_ERR(inode)) {
> > > > + if (file && (file->f_flags & OPENAT2_REGULAR) && !S_ISREG(inode->i_mode)) {
> > >
> > > Isn't OPENAT2_REGULAR getting masked off in ->f_flags now?
> > >
> > Yes, I thought the masking off was happening after this codepath got
> > executed. Maybe it's better anyway to pass another flags param to this
> > function and forward the flags from the gfs2_atomic_open function and
> > in other call sites pass 0 ? What do you think?
> >
>
> Also my mistake. That happens in do_dentry_open() which happens in
> finish_open(), so you should be OK here.
>
> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>

Thanks for patiently reviewing this! I am planning on sending patches
for man-pages and looking into some xfs-tests for this. But I am not
sure if this patch series will get more reviews from others or if it
will be picked up in the vfs branch?

Regards,
Dorjoy