From: Andrii Nakryiko <andriin@fb.com>
Date: Thu, 3 Sep 2020 20:35:29 +0000 (-0700)
Subject: libbpf: Ensure ELF symbols table is found before further ELF processing
X-Git-Tag: v5.10-rc1~107^2~169^2~57^2~13
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0201c575831171292489f14a8b6f79f98936b4d1;p=thirdparty%2Fkernel%2Flinux.git

libbpf: Ensure ELF symbols table is found before further ELF processing

libbpf ELF parsing logic might need symbols available before ELF parsing is
completed, so we need to make sure that symbols table section is found in
a separate pass before all the subsequent sections are processed.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200903203542.15944-2-andriin@fb.com
---

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b688aadf09c5d..ac56d4db6d3ed 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2720,14 +2720,38 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 	Elf *elf = obj->efile.elf;
 	Elf_Data *btf_ext_data = NULL;
 	Elf_Data *btf_data = NULL;
-	Elf_Scn *scn = NULL;
 	int idx = 0, err = 0;
+	const char *name;
+	Elf_Data *data;
+	Elf_Scn *scn;
+	GElf_Shdr sh;
 
+	/* a bunch of ELF parsing functionality depends on processing symbols,
+	 * so do the first pass and find the symbol table
+	 */
+	scn = NULL;
 	while ((scn = elf_nextscn(elf, scn)) != NULL) {
-		const char *name;
-		GElf_Shdr sh;
-		Elf_Data *data;
+		if (elf_sec_hdr(obj, scn, &sh))
+			return -LIBBPF_ERRNO__FORMAT;
+
+		if (sh.sh_type == SHT_SYMTAB) {
+			if (obj->efile.symbols) {
+				pr_warn("elf: multiple symbol tables in %s\n", obj->path);
+				return -LIBBPF_ERRNO__FORMAT;
+			}
 
+			data = elf_sec_data(obj, scn);
+			if (!data)
+				return -LIBBPF_ERRNO__FORMAT;
+
+			obj->efile.symbols = data;
+			obj->efile.symbols_shndx = elf_ndxscn(scn);
+			obj->efile.strtabidx = sh.sh_link;
+		}
+	}
+
+	scn = NULL;
+	while ((scn = elf_nextscn(elf, scn)) != NULL) {
 		idx++;
 
 		if (elf_sec_hdr(obj, scn, &sh))
@@ -2766,13 +2790,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 		} else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
 			btf_ext_data = data;
 		} else if (sh.sh_type == SHT_SYMTAB) {
-			if (obj->efile.symbols) {
-				pr_warn("elf: multiple symbol tables in %s\n", obj->path);
-				return -LIBBPF_ERRNO__FORMAT;
-			}
-			obj->efile.symbols = data;
-			obj->efile.symbols_shndx = idx;
-			obj->efile.strtabidx = sh.sh_link;
+			/* already processed during the first pass above */
 		} else if (sh.sh_type == SHT_PROGBITS && data->d_size > 0) {
 			if (sh.sh_flags & SHF_EXECINSTR) {
 				if (strcmp(name, ".text") == 0)