libbpf: Detect corrupted ELF symbols section

Prevent divide-by-zero if ELF is corrupted and has zero sh_entsize.
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/20211103173213.1376990-2-andrii@kernel.org

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a1bea1953df6739a10d49a3824ea66cc768ef31a..71f5a009010a92f88ad9eb3bf5ec9a14cf194e9f 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3555,7 +3555,7 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
 
        scn = elf_sec_by_idx(obj, obj->efile.symbols_shndx);
        sh = elf_sec_hdr(obj, scn);
-       if (!sh)
+       if (!sh || sh->sh_entsize != sizeof(Elf64_Sym))
                return -LIBBPF_ERRNO__FORMAT;
 
        dummy_var_btf_id = add_dummy_ksym_var(obj->btf);