libbpf: Sanitise map names before pinning

When we added sanitising of map names before loading programs to libbpf, we
still allowed periods in the name. While the kernel will accept these for
the map names themselves, they are not allowed in file names when pinning
maps. This means that bpf_object__pin_maps() will fail if called on an
object that contains internal maps (such as sections .rodata).

Fix this by replacing periods with underscores when constructing map pin
paths. This only affects the paths generated by libbpf when
bpf_object__pin_maps() is called with a path argument. Any pin paths set
by bpf_map__set_pin_path() are unaffected, and it will still be up to the
caller to avoid invalid characters in those.

Fixes: 113e6b7e15 ("libbpf: Sanitise internal map names so they are not rejected by the kernel")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201203093306.107676-1-toke@redhat.com

tools/lib/bpf/libbpf.c

@@ -7659,6 +7659,16 @@ bool bpf_map__is_pinned(const struct bpf_map *map)
 	return map->pinned;
 }
 
+static void sanitize_pin_path(char *s)
+{
+	/* bpffs disallows periods in path names */
+	while (*s) {
+		if (*s == '.')
+			*s = '_';
+		s++;
+	}
+}
+
 int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
 {
 	struct bpf_map *map;
@@ -7688,6 +7698,7 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
 				err = -ENAMETOOLONG;
 				goto err_unpin_maps;
 			}
+			sanitize_pin_path(buf);
 			pin_path = buf;
 		} else if (!map->pin_path) {
 			continue;
@@ -7732,6 +7743,7 @@ int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
 				return -EINVAL;
 			else if (len >= PATH_MAX)
 				return -ENAMETOOLONG;
+			sanitize_pin_path(buf);
 			pin_path = buf;
 		} else if (!map->pin_path) {
 			continue;