[PATCH AUTOSEL 5.4 21/22] libbpf: Add NULL checks to bpf_object__{prev_map,next_map}

[Sasha Levin]

From: Andreas Ziegler <ziegler.andreas@xxxxxxxxxxx>

[ 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@xxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20240703083436.505124-1-ziegler.andreas@xxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b8849812449c3..98e34c5172673 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4754,7 +4754,7 @@ __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);
@@ -4763,7 +4763,7 @@ 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;
-- 
2.43.0