diff options
| author | Jori Koolstra <jkoolstra@xs4all.nl> | 2026-04-24 13:46:02 +0200 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2026-05-21 10:53:33 +0200 |
| commit | 31cf44efa6df72a524b40adefb80539f3a4e13ba (patch) | |
| tree | 7ff56857adc3f9756dce98b28a7179256aeac61d | |
| parent | 3e0be8ccff090cde4e10410f8e6a3fefeeff4124 (diff) | |
vfs: add O_EMPTYPATH to openat(2)/openat2(2)
To get an operable version of an O_PATH file descriptor, it is possible
to use openat(fd, ".", O_DIRECTORY) for directories, but other files
currently require going through open("/proc/<pid>/fd/<nr>"), which
depends on a functioning procfs.
This patch adds the O_EMPTYPATH flag to openat(2)/openat2(2). If passed,
LOOKUP_EMPTY is set at path resolution time.
Note: This implies that you cannot rely anymore on disabling procfs from
being mounted (e.g. inside a container without procfs mounted and with
CAP_SYS_ADMIN dropped) to prevent O_PATH fds from being re-opened
read-write.
Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
Link: https://patch.msgid.link/20260424114611.1678641-2-jkoolstra@xs4all.nl
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
| -rw-r--r-- | fs/fcntl.c | 2 | ||||
| -rw-r--r-- | fs/open.c | 6 | ||||
| -rw-r--r-- | include/linux/fcntl.h | 2 | ||||
| -rw-r--r-- | 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 beab8080badf..7d2165855a9c 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 681d405bc61e..9e0164a8c1fb 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1158,7 +1158,7 @@ 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_EMPTYPATH) inline struct open_how build_open_how(int flags, umode_t mode) { @@ -1279,6 +1279,8 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op) lookup_flags |= LOOKUP_DIRECTORY; if (!(flags & O_NOFOLLOW)) lookup_flags |= LOOKUP_FOLLOW; + if (flags & O_EMPTYPATH) + lookup_flags |= LOOKUP_EMPTY; if (how->resolve & RESOLVE_NO_XDEV) lookup_flags |= LOOKUP_NO_XDEV; @@ -1360,7 +1362,7 @@ 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..c65c5c73d362 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_TMPFILE | O_EMPTYPATH) /* 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..bfc68156b45a 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_EMPTYPATH +#define O_EMPTYPATH (1 << 26) /* allow empty path */ +#endif + /* a horrid kludge trying to make sure that this will fail on old kernels */ #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) |