Commit 4aadd292 authored May 25, 2023 by Andrii Nakryiko Committed by Daniel Borkmann May 26, 2023

libbpf: Ensure FD >= 3 during bpf_map__reuse_fd()



Improve bpf_map__reuse_fd() logic and ensure that dup'ed map FD is
"good" (>= 3) and has O_CLOEXEC flags. Use fcntl(F_DUPFD_CLOEXEC) for
that, similarly to ensure_good_fd() helper we already use in low-level
APIs that work with bpf() syscall.

Suggested-by: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230525221311.2136408-2-andrii@kernel.org

parent 59842c54

tools/lib/bpf/libbpf.c

+6 −7

Original line number	Diff line number	Diff line
		@@ -4414,18 +4414,17 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
		if (!new_name)
		return libbpf_err(-errno);

		new_fd = open("/", O_RDONLY \| O_CLOEXEC);
		/*
		* Like dup(), but make sure new FD is >= 3 and has O_CLOEXEC set.
		* This is similar to what we do in ensure_good_fd(), but without
		* closing original FD.
		*/
		new_fd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
		if (new_fd < 0) {
		err = -errno;
		goto err_free_new_name;
		}

		new_fd = dup3(fd, new_fd, O_CLOEXEC);
		if (new_fd < 0) {
		err = -errno;
		goto err_close_new_fd;
		}

		err = zclose(map->fd);
		if (err) {
		err = -errno;