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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483b8196ae0sm447875e9.0.2026.02.23.08.45.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Feb 2026 08:45:12 -0800 (PST) Date: Mon, 23 Feb 2026 16:45:11 +0000 From: David Laight To: Jori Koolstra Cc: jlayton@kernel.org, chuck.lever@oracle.com, alex.aring@gmail.com, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, arnd@arndb.de, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [PATCH] Add support for empty path in openat and openat2 syscalls Message-ID: <20260223164511.525762fb@pumpkin> In-Reply-To: <20260223151652.582048-1-jkoolstra@xs4all.nl> References: <20260223151652.582048-1-jkoolstra@xs4all.nl> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 23 Feb 2026 16:16:52 +0100 Jori Koolstra wrote: > To get an operable version of an O_PATH file descriptors, it is possible > to use openat(fd, ".", O_DIRECTORY) for directories, but other files > currently require going through open("/proc//fd/") which > depends on a functioning procfs. What do you want the fd for? There are good reasons for wanting an fd for a directory that you don't have access permissions for, but what is the use case for a file? It all gets very close to letting you do things that the 'security model' should reject. David > > This patch adds the O_EMPTY_PATH flag to openat and openat2. If passed > LOOKUP_EMPTY is set at path resolve time. > > Signed-off-by: Jori Koolstra > --- > fs/fcntl.c | 2 +- > fs/open.c | 6 ++++-- > include/linux/fcntl.h | 2 +- > include/uapi/asm-generic/fcntl.h | 4 ++++ > 4 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/fs/fcntl.c b/fs/fcntl.c > index f93dbca08435..62ab4ad2b6f5 100644 > --- a/fs/fcntl.c > +++ b/fs/fcntl.c > @@ -1169,7 +1169,7 @@ 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)) | > __FMODE_EXEC)); > diff --git a/fs/open.c b/fs/open.c > index 91f1139591ab..32865822ca1c 100644 > --- a/fs/open.c > +++ b/fs/open.c > @@ -1160,7 +1160,7 @@ struct file *kernel_file_open(const struct path *path, int flags, > EXPORT_SYMBOL_GPL(kernel_file_open); > > #define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE)) > -#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC) > +#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC | O_EMPTY_PATH) > > inline struct open_how build_open_how(int flags, umode_t mode) > { > @@ -1277,6 +1277,8 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op) > } > } > > + if (flags & O_EMPTY_PATH) > + lookup_flags |= LOOKUP_EMPTY; > if (flags & O_DIRECTORY) > lookup_flags |= LOOKUP_DIRECTORY; > if (!(flags & O_NOFOLLOW)) > @@ -1362,7 +1364,7 @@ static int do_sys_openat2(int dfd, const char __user *filename, > if (unlikely(err)) > return err; > > - CLASS(filename, name)(filename); > + CLASS(filename_flags, name)(filename, op.lookup_flags); > return FD_ADD(how->flags, do_file_open(dfd, name, &op)); > } > > diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h > index a332e79b3207..ce742f67bf60 100644 > --- a/include/linux/fcntl.h > +++ b/include/linux/fcntl.h > @@ -10,7 +10,7 @@ > (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \ > O_APPEND | O_NDELAY | O_NONBLOCK | __O_SYNC | O_DSYNC | \ > FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ > - O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) > + O_NOATIME | O_CLOEXEC | O_PATH | O_EMPTY_PATH | __O_TMPFILE) > > /* List of all valid flags for the how->resolve argument: */ > #define VALID_RESOLVE_FLAGS \ > diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h > index 613475285643..8e4e796ad212 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 O_EMPTY_PATH > +#define O_EMPTY_PATH 0100000000 > +#endif > + > /* a horrid kludge trying to make sure that this will fail on old kernels */ > #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) >