libbpf: Fix BTF data layout checks and allow empty BTF

Make data section layout checks stricter, disallowing overlap of types and
strings data.

Additionally, allow BTFs with no type data. There is nothing inherently wrong
with having BTF with no types (put potentially with some strings). This could
be a situation with kernel module BTFs, if module doesn't introduce any new
type information.

Also fix invalid offset alignment check for btf->hdr->type_off.

Fixes: 8a138aed4a80 ("bpf: btf: Add BTF support to libbpf")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201105043402.2530976-8-andrii@kernel.org

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 0258cf108c0a5b90cf40bc591b3059e4f1f235fb..20bb88e71f072c259f63a2b3b58a405ced6db7ba 100644 (file)
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -245,22 +245,18 @@ static int btf_parse_hdr(struct btf *btf)
                return -EINVAL;
        }
 
-       if (meta_left < hdr->type_off) {
-               pr_debug("Invalid BTF type section offset:%u\n", hdr->type_off);
+       if (meta_left < hdr->str_off + hdr->str_len) {
+               pr_debug("Invalid BTF total size:%u\n", btf->raw_size);
                return -EINVAL;
        }
 
-       if (meta_left < hdr->str_off) {
-               pr_debug("Invalid BTF string section offset:%u\n", hdr->str_off);
+       if (hdr->type_off + hdr->type_len > hdr->str_off) {
+               pr_debug("Invalid BTF data sections layout: type data at %u + %u, strings data at %u + %u\n",
+                        hdr->type_off, hdr->type_len, hdr->str_off, hdr->str_len);
                return -EINVAL;
        }
 
-       if (hdr->type_off >= hdr->str_off) {
-               pr_debug("BTF type section offset >= string section offset. No type?\n");
-               return -EINVAL;
-       }
-
-       if (hdr->type_off & 0x02) {
+       if (hdr->type_off % 4) {
                pr_debug("BTF type section is not aligned to 4 bytes\n");
                return -EINVAL;
        }