On Sun, Mar 1, 2026 at 6:44 PM Jeff Layton <[email protected]> wrote: > > 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. >
Good suggestion. Yes, I can include this information in the commit message during the next posting. > 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. > I used virtme-ng (which I think reuses the host's filesystem) to run the compiled bzImage and ran the openat2 kselftests there to verify it's working. Is there a similar way I can test NFS/SMB by adding kselftests? Or would I need to setup NFS/SMB inside a full VM distro with a modified kernel to test this? I would appreciate any suggestion on this. > 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. > Good point. There was a comment in a previous posting of this patch series "The most useful behavior would indicate what was found (e.g., a pipe)." (ref: https://lore.kernel.org/linux-fsdevel/vhq3osjqs3nn764wrp2lxp66b4dxpb3n5x3dijhe2yr53qfgy3@tfswbjskc3y6/ ) So I thought maybe it would be useful to return -EISDIR where it was already doing that. But it is a good point about consistency that we won't be doing this for other different types so I guess it's better to return -EFTYPE for all the cases anyway as you mention. Any thoughts? > 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. > Are the manpages in the kernel git repository or in a separate repository? Do I make separate patch series for that? Sorry I don't know about this in detail. > > 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 <[email protected]> > > --- > > 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? > Yes, I thought it would be useful for the caller to know what type of file it actually is so I had kept this the same. Let me know if it is preferable to return -EFTYPE always. Thanks for reviewing! Regards, Dorjoy
