libbpf: Validate that .BTF and .BTF.ext sections contain data

.BTF and .BTF.ext ELF sections should have SHT_PROGBITS type and contain
data. If they are not, ELF is invalid or corrupted, so bail out.
Otherwise this can lead to data->d_buf being NULL and SIGSEGV later on.
Reported by oss-fuzz project.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211103173213.1376990-4-andrii@kernel.org

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f836a19..0dc6465 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3270,8 +3270,12 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                } else if (strcmp(name, MAPS_ELF_SEC) == 0) {
                        obj->efile.btf_maps_shndx = idx;
                } else if (strcmp(name, BTF_ELF_SEC) == 0) {
+                       if (sh->sh_type != SHT_PROGBITS)
+                               return -LIBBPF_ERRNO__FORMAT;
                        btf_data = data;
                } else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
+                       if (sh->sh_type != SHT_PROGBITS)
+                               return -LIBBPF_ERRNO__FORMAT;
                        btf_ext_data = data;
                } else if (sh->sh_type == SHT_SYMTAB) {
                        /* already processed during the first pass above */