Commit b7332d28 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: Improve ELF relo sanitization 



Add few sanity checks for relocations to prevent div-by-zero and
out-of-bounds array accesses in libbpf.

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211103173213.1376990-6-andrii@kernel.org
parent 0d6988e1

tools/lib/bpf/libbpf.c

+19 −5
Original line number Diff line number Diff line
@@ -3306,6 +3306,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj) 
		} else if (sh->sh_type == SHT_REL) {

			int targ_sec_idx = sh->sh_info; /* points to other section */



			if (sh->sh_entsize != sizeof(Elf64_Rel) ||

			    targ_sec_idx >= obj->efile.sec_cnt)

				return -LIBBPF_ERRNO__FORMAT;



			/* Only do relo for section with exec instructions */

			if (!section_have_execinstr(obj, targ_sec_idx) &&

			    strcmp(name, ".rel" STRUCT_OPS_SEC) &&
@@ -4025,7 +4029,7 @@ static int 
bpf_object__collect_prog_relos(struct bpf_object *obj, Elf64_Shdr *shdr, Elf_Data *data)

{

	const char *relo_sec_name, *sec_name;

	size_t sec_idx = shdr->sh_info;

	size_t sec_idx = shdr->sh_info, sym_idx;

	struct bpf_program *prog;

	struct reloc_desc *relos;

	int err, i, nrels;
@@ -4036,6 +4040,9 @@ bpf_object__collect_prog_relos(struct bpf_object *obj, Elf64_Shdr *shdr, Elf_Dat 
	Elf64_Sym *sym;

	Elf64_Rel *rel;



	if (sec_idx >= obj->efile.sec_cnt)

		return -EINVAL;



	scn = elf_sec_by_idx(obj, sec_idx);

	scn_data = elf_sec_data(obj, scn);
@@ -4055,16 +4062,23 @@ bpf_object__collect_prog_relos(struct bpf_object *obj, Elf64_Shdr *shdr, Elf_Dat 
			return -LIBBPF_ERRNO__FORMAT;

		}



		sym = elf_sym_by_idx(obj, ELF64_R_SYM(rel->r_info));

		sym_idx = ELF64_R_SYM(rel->r_info);

		sym = elf_sym_by_idx(obj, sym_idx);

		if (!sym) {

			pr_warn("sec '%s': symbol 0x%zx not found for relo #%d\n",

				relo_sec_name, (size_t)ELF64_R_SYM(rel->r_info), i);

			pr_warn("sec '%s': symbol #%zu not found for relo #%d\n",

				relo_sec_name, sym_idx, i);

			return -LIBBPF_ERRNO__FORMAT;

		}



		if (sym->st_shndx >= obj->efile.sec_cnt) {

			pr_warn("sec '%s': corrupted symbol #%zu pointing to invalid section #%zu for relo #%d\n",

				relo_sec_name, sym_idx, (size_t)sym->st_shndx, i);

			return -LIBBPF_ERRNO__FORMAT;

		}



		if (rel->r_offset % BPF_INSN_SZ || rel->r_offset >= scn_data->d_size) {

			pr_warn("sec '%s': invalid offset 0x%zx for relo #%d\n",

				relo_sec_name, (size_t)ELF64_R_SYM(rel->r_info), i);

				relo_sec_name, (size_t)rel->r_offset, i);

			return -LIBBPF_ERRNO__FORMAT;

		}