tc, bpf: check section names and type everywhere

When extracting sections, we better check for name and type. Noticed
that some llvm versions emit .strtab and .shstrtab (e.g. saw it on pre
3.7), while more recent ones only seem to emit .strtab. Thus, make sure
we get the right sections.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>

tc/tc_bpf.c

@@ -1237,14 +1237,17 @@ static int bpf_fetch_ancillary(struct bpf_elf_ctx *ctx)
 		if (ret < 0)
 			continue;
 
-		if (!strcmp(data.sec_name, ELF_SECTION_MAPS))
+		if (data.sec_hdr.sh_type == SHT_PROGBITS &&
+		    !strcmp(data.sec_name, ELF_SECTION_MAPS))
 			ret = bpf_fetch_maps(ctx, i, &data);
-		else if (!strcmp(data.sec_name, ELF_SECTION_LICENSE))
+		else if (data.sec_hdr.sh_type == SHT_PROGBITS &&
+			 !strcmp(data.sec_name, ELF_SECTION_LICENSE))
 			ret = bpf_fetch_license(ctx, i, &data);
-		else if (data.sec_hdr.sh_type == SHT_SYMTAB)
+		else if (data.sec_hdr.sh_type == SHT_SYMTAB &&
+			 !strcmp(data.sec_name, ".symtab"))
 			ret = bpf_fetch_symtab(ctx, i, &data);
 		else if (data.sec_hdr.sh_type == SHT_STRTAB &&
-			 i != ctx->elf_hdr.e_shstrndx)
+			 !strcmp(data.sec_name, ".strtab"))
 			ret = bpf_fetch_strtab(ctx, i, &data);
 		if (ret < 0) {
 			fprintf(stderr, "Error parsing section %d! Perhaps"
@@ -1275,7 +1278,10 @@ static int bpf_fetch_prog(struct bpf_elf_ctx *ctx, const char *section)
 			continue;
 
 		ret = bpf_fill_section_data(ctx, i, &data);
-		if (ret < 0 || strcmp(data.sec_name, section))
+		if (ret < 0 ||
+		    !(data.sec_hdr.sh_type == SHT_PROGBITS &&
+		      data.sec_hdr.sh_flags & SHF_EXECINSTR &&
+		      !strcmp(data.sec_name, section)))
 			continue;
 
 		memset(&prog, 0, sizeof(prog));
@@ -1353,7 +1359,10 @@ static int bpf_fetch_prog_relo(struct bpf_elf_ctx *ctx, const char *section)
 
 		idx = data_relo.sec_hdr.sh_info;
 		ret = bpf_fill_section_data(ctx, idx, &data_insn);
-		if (ret < 0 || strcmp(data_insn.sec_name, section))
+		if (ret < 0 ||
+		    !(data_insn.sec_hdr.sh_type == SHT_PROGBITS &&
+		      data_insn.sec_hdr.sh_flags & SHF_EXECINSTR &&
+		      !strcmp(data_insn.sec_name, section)))
 			continue;
 
 		ret = bpf_apply_relo_data(ctx, &data_relo, &data_insn);