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

[Jeff Layton <jlayton@kernel.org>]

On Sat, 2026-04-04 at 21:17 +0600, Dorjoy Chowdhury wrote:
> On Thu, Apr 2, 2026 at 1:02 AM Jeff Layton <jlayton@kernel.org> 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@kernel.org> 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@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/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@kernel.org>
> 
> 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?
> 

This is a change to rather core VFS infrastructure so yes, you should
expect some more review. Assuming no major issues are found, then yes,
this should eventually get picked up by the VFS maintainers.

Cheers,
-- 
Jeff Layton <jlayton@kernel.org>