libbpf: Fix BTF header parsing checks

Original code assumed fixed and correct BTF header length. That's not
always the case, though, so fix this bug with a proper additional check.
And use actual header length instead of sizeof(struct btf_header) in
sanity checks.

Fixes: 8a138aed4a80 ("bpf: btf: Add BTF support to libbpf")
Reported-by: Evgeny Vereshchagin <evvers@ya.ru>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211023003157.726961-2-andrii@kernel.org

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 05b9452088154d9645649b1284b3c0df4d10b320..ef924fc2c911430d902aa85efcc8c95c5e928739 100644 (file)
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -236,13 +236,19 @@ static int btf_parse_hdr(struct btf *btf)
                }
                btf_bswap_hdr(hdr);
        } else if (hdr->magic != BTF_MAGIC) {
-               pr_debug("Invalid BTF magic:%x\n", hdr->magic);
+               pr_debug("Invalid BTF magic: %x\n", hdr->magic);
                return -EINVAL;
        }
 
-       meta_left = btf->raw_size - sizeof(*hdr);
+       if (btf->raw_size < hdr->hdr_len) {
+               pr_debug("BTF header len %u larger than data size %u\n",
+                        hdr->hdr_len, btf->raw_size);
+               return -EINVAL;
+       }
+
+       meta_left = btf->raw_size - hdr->hdr_len;
        if (meta_left < (long long)hdr->str_off + hdr->str_len) {
-               pr_debug("Invalid BTF total size:%u\n", btf->raw_size);
+               pr_debug("Invalid BTF total size: %u\n", btf->raw_size);
                return -EINVAL;
        }