libbpf: Verify section type in btf_find_elf_sections

A valid ELF file may contain a SHT_NOBITS .BTF section. This case is
not handled correctly in btf_parse_elf, which leads to a segfault.

Before attempting to load BTF section data, check that the section
type is SHT_PROGBITS, which is the expected type for BTF data.  Fail
with an error if the type is different.

Bug report: libbpf/libbpf#894
v1: https://lore.kernel.org/bpf/[email protected]/

Signed-off-by: Ihor Solodrai <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: theihor

tools/lib/bpf/btf.c

@@ -1148,6 +1148,12 @@ static int btf_find_elf_sections(Elf *elf, const char *path, struct btf_elf_secs
 		else
 			continue;
 
+		if (sh.sh_type != SHT_PROGBITS) {
+			pr_warn("unexpected section type (%d) of section(%d, %s) from %s\n",
+				sh.sh_type, idx, name, path);
+			goto err;
+		}
+
 		data = elf_getdata(scn, 0);
 		if (!data) {
 			pr_warn("failed to get section(%d, %s) data from %s\n",