On Tue, 2024-08-06 at 10:38 -0700, Yonghong Song wrote:

On 8/6/24 3:51 AM, Ma Ke wrote:

...

To prevent potential error return values, it is necessary to check the return value of btf__type_by_id. We can add a kind checking to fix the issue.

Cc: stable@vger.kernel.org Fixes: 430025e5dca5 ("libbpf: Add subskeleton scaffolding") Signed-off-by: Ma Ke make24@iscas.ac.cn

---

tools/lib/bpf/libbpf.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index a3be6f8fac09..d1eb45d16054 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -13850,6 +13850,9 @@ int bpf_object__open_subskeleton(struct bpf_object_subskeleton *s) var = btf_var_secinfos(map_type); for (i = 0; i < len; i++, var++) { var_type = btf__type_by_id(btf, var->type);

• 	if (!var_type)
  

• 		return libbpf_err(-ENOENT);
  

Could you give a detailed example when this error could be triggered?

I'm curious as well, tools/lib/bpf/btf.c:btf_validate_type() has the following code:

static int btf_validate_type(const struct btf *btf, const struct btf_type *t, __u32 id) { ... switch (kind) { ... case ... case BTF_KIND_VAR: case ... err = btf_validate_id(btf, t->type, id); if (err) return err; break;

That should catch situations exactly like this one.

...

• var_name = btf__name_by_offset(btf, var_type->name_off);
  if (strcmp(var_name, var_skel->name) == 0) {
  	*var_skel->addr = map->mmaped + var->offset;