bpf: Use proper target btf when exporting attach_btf_obj_id

When attaching to program, the program itself might not be attached
to anything (and, hence, might not have attach_btf), so we can't
unconditionally use 'prog->aux->dst_prog->aux->attach_btf'.

Instead, use bpf_prog_get_target_btf to pick proper target BTF:

  * when attached to dst_prog, use dst_prog->aux->btf
  * when attached to kernel btf, use prog->aux->attach_btf

Fixes: b79c9fc9551b ("bpf: implement BPF_PROG_QUERY for BPF_LSM_CGROUP")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Hao Luo <haoluo@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220804201140.1340684-1-sdf@google.com

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 83c7136..7dc3f80 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3886,6 +3886,7 @@ static int bpf_prog_get_info_by_fd(struct file *file,
                                   union bpf_attr __user *uattr)
 {
        struct bpf_prog_info __user *uinfo = u64_to_user_ptr(attr->info.info);
+       struct btf *attach_btf = bpf_prog_get_target_btf(prog);
        struct bpf_prog_info info;
        u32 info_len = attr->info.info_len;
        struct bpf_prog_kstats stats;
@@ -4088,10 +4089,8 @@ static int bpf_prog_get_info_by_fd(struct file *file,
        if (prog->aux->btf)
                info.btf_id = btf_obj_id(prog->aux->btf);
        info.attach_btf_id = prog->aux->attach_btf_id;
-       if (prog->aux->attach_btf)
-               info.attach_btf_obj_id = btf_obj_id(prog->aux->attach_btf);
-       else if (prog->aux->dst_prog)
-               info.attach_btf_obj_id = btf_obj_id(prog->aux->dst_prog->aux->attach_btf);
+       if (attach_btf)
+               info.attach_btf_obj_id = btf_obj_id(attach_btf);
 
        ulen = info.nr_func_info;
        info.nr_func_info = prog->aux->func_info_cnt;