libbpf: Add NULL checks to bpf_object__{prev_map,next_map}

[ Upstream commit cedc12c5b57f7efa6dbebfb2b140e8675f5a2616 ]

In the current state, an erroneous call to
bpf_object__find_map_by_name(NULL, ...) leads to a segmentation
fault through the following call chain:

  bpf_object__find_map_by_name(obj = NULL, ...)
  -> bpf_object__for_each_map(pos, obj = NULL)
  -> bpf_object__next_map((obj = NULL), NULL)
  -> return (obj = NULL)->maps

While calling bpf_object__find_map_by_name with obj = NULL is
obviously incorrect, this should not lead to a segmentation
fault but rather be handled gracefully.

As __bpf_map__iter already handles this situation correctly, we
can delegate the check for the regular case there and only add
a check in case the prev or next parameter is NULL.

Signed-off-by: Andreas Ziegler <ziegler.andreas@siemens.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240703083436.505124-1-ziegler.andreas@siemens.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 015ed8253f739ba4b09ed431109825afd8f24abf..33cdcfe10634488ddf6d96816dc6df182751d400 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9005,7 +9005,7 @@ __bpf_map__iter(const struct bpf_map *m, const struct bpf_object *obj, int i)
 struct bpf_map *
 bpf_map__next(const struct bpf_map *prev, const struct bpf_object *obj)
 {
-       if (prev == NULL)
+       if (prev == NULL && obj != NULL)
                return obj->maps;
 
        return __bpf_map__iter(prev, obj, 1);
@@ -9014,7 +9014,7 @@ bpf_map__next(const struct bpf_map *prev, const struct bpf_object *obj)
 struct bpf_map *
 bpf_map__prev(const struct bpf_map *next, const struct bpf_object *obj)
 {
-       if (next == NULL) {
+       if (next == NULL && obj != NULL) {
                if (!obj->nr_maps)
                        return NULL;
                return obj->maps + obj->nr_maps - 1;