libbpf: Prevent double close and leak of btf objects

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>
Link: https://lore.kernel.org/r/20260416100034.1610852-1-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8b0c3246097f5c0f06b94c5dac5d11f5c8240a30..3a80a018fc7d50cb613c62e6b9423739a2794150 100644 (file)
--- 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 *