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vfs: add O_EMPTYPATH to openat(2)/openat2(2)

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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>
This commit is contained in:
Jori Koolstra
2026-04-24 13:46:02 +02:00
committed by Christian Brauner
parent 3e0be8ccff
commit 31cf44efa6
4 changed files with 10 additions and 4 deletions
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4
include/uapi/asm-generic/fcntl.h
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@@ -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)