[PATCHv3 bpf] libbpf: Prevent double close and leak of btf objects

[Jiri Olsa <jolsa@kernel.org>]

Sashiko found possible double close of btf object fd [1],
which happens when strdup in load_module_btfs fails at which
point the obj->btf_module_cnt is already incremented.

The error path close btf fd and so does later cleanup code in
bpf_object_post_load_cleanup function.

Also libbpf_ensure_mem failure leaves btf object not assigned
and it's leaked.

Replacing the err_out label with break to make the error path
less confusing as suggested by Alan.

Incrementing obj->btf_module_cnt only if there's no failure
and releasing btf object in error path.

Fixes: 91abb4a6d79d ("libbpf: Support attachment of BPF tracing programs to kernel modules")
[1] https://sashiko.dev/#/patchset/20260324081846.2334094-1-jolsa%40kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
v2: https://lore.kernel.org/bpf/20260415082452.1489147-1-jolsa@kernel.org/

v3 changes:
- replacing the err_out label with break [Alan]
- subject change [Alan]

 tools/lib/bpf/libbpf.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8b0c3246097f..3a80a018fc7d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5852,11 +5852,12 @@ static int load_module_btfs(struct bpf_object *obj)
 		info.name = ptr_to_u64(name);
 		info.name_len = sizeof(name);
 
+		btf = NULL;
 		err = bpf_btf_get_info_by_fd(fd, &info, &len);
 		if (err) {
 			err = -errno;
 			pr_warn("failed to get BTF object #%d info: %s\n", id, errstr(err));
-			goto err_out;
+			break;
 		}
 
 		/* ignore non-module BTFs */
@@ -5870,15 +5871,15 @@ static int load_module_btfs(struct bpf_object *obj)
 		if (err) {
 			pr_warn("failed to load module [%s]'s BTF object #%d: %s\n",
 				name, id, errstr(err));
-			goto err_out;
+			break;
 		}
 
 		err = libbpf_ensure_mem((void **)&obj->btf_modules, &obj->btf_module_cap,
 					sizeof(*obj->btf_modules), obj->btf_module_cnt + 1);
 		if (err)
-			goto err_out;
+			break;
 
-		mod_btf = &obj->btf_modules[obj->btf_module_cnt++];
+		mod_btf = &obj->btf_modules[obj->btf_module_cnt];
 
 		mod_btf->btf = btf;
 		mod_btf->id = id;
@@ -5886,16 +5887,16 @@ static int load_module_btfs(struct bpf_object *obj)
 		mod_btf->name = strdup(name);
 		if (!mod_btf->name) {
 			err = -ENOMEM;
-			goto err_out;
+			break;
 		}
-		continue;
+		obj->btf_module_cnt++;
+	}
 
-err_out:
+	if (err) {
+		btf__free(btf);
 		close(fd);
-		return err;
 	}
-
-	return 0;
+	return err;
 }
 
 static struct bpf_core_cand_list *
-- 
2.53.0