bpf: btf: Add BPF_OBJ_GET_INFO_BY_FD support to BTF fd

This patch adds BPF_OBJ_GET_INFO_BY_FD support to BTF fd.
The original BTF data, which was used to create the BTF fd during
the earlier BPF_BTF_LOAD call, will be returned.

The userspace is expected to allocate buffer
to info.info and the buffer size is set to info.info_len before
calling BPF_OBJ_GET_INFO_BY_FD.

The original BTF data is copied to the userspace buffer (info.info).
Only upto the user's specified info.info_len will be copied.

The original BTF data size is set to info.info_len.  The userspace
needs to check if it is bigger than its allocated buffer size.
If it is, the userspace should realloc with the kernel-returned
info.info_len and call the BPF_OBJ_GET_INFO_BY_FD again.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cd8ebadc66eb..0a4924a0a8da 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2017,6 +2017,8 @@ static int bpf_obj_get_info_by_fd(const union bpf_attr *attr,
         else if (f.file->f_op == &bpf_map_fops)
                 err = bpf_map_get_info_by_fd(f.file->private_data, attr,
                                              uattr);
+        else if (f.file->f_op == &btf_fops)
+                err = btf_get_info_by_fd(f.file->private_data, attr, uattr);
         else
                 err = -EINVAL;