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libbpf: Ensure FD >= 3 during bpf_map__reuse_fd()

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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
This commit is contained in:
Andrii Nakryiko 2023-05-25 15:13:11 -07:00 committed by Daniel Borkmann
parent 59842c5451
commit 4aadd2920b
1 changed files with 6 additions and 7 deletions
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13
tools/lib/bpf/libbpf.c
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@ -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;