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.

Jori Koolstra committed 6 months ago

Commit 31cf44e1 parent 3e0be8c4 files · +10 −4Browse files

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include/uapi/asm-generic/fcntl.h+4−0

@@ -88,6 +88,10 @@ · 87 unmodified lines
88	88	#define __O_TMPFILE 020000000
89	89	#endif
90	90
	91	+#ifndef O_EMPTYPATH
	92	+#define O_EMPTYPATH (1 << 26) /* allow empty path */
	93	+#endif
	94	+
91	95	/* a horrid kludge trying to make sure that this will fail on old kernels */
92	96	#define O_TMPFILE (__O_TMPFILE \| O_DIRECTORY)
93	97