libbpf: Fix using invalidated memory in bpf_linker

add_dst_sec() can invalidate bpf_linker's section index making dst_symtab pointer pointing into unallocated memory. Reinitialize dst_symtab pointer on each iteration to make sure it's always valid. Fixes: faf6ed3 ("libbpf: Add BPF static linker APIs") Signed-off-by: Andrii Nakryiko <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]> Link: https://lore.kernel.org/bpf/[email protected]
okias · Nov 25, 2021 · 5938353 · 5938353
1 parent 8cb1255
commit 5938353
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
@@ -2000,7 +2000,7 @@ static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj)
 {
 	struct src_sec *src_symtab = &obj->secs[obj->symtab_sec_idx];
-	struct dst_sec *dst_symtab = &linker->secs[linker->symtab_sec_idx];
+	struct dst_sec *dst_symtab;
 	int i, err;
 
 	for (i = 1; i < obj->sec_cnt; i++) {
@@ -2033,6 +2033,9 @@ static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *ob
 			return -1;
 		}
 
+		/* add_dst_sec() above could have invalidated linker->secs */
+		dst_symtab = &linker->secs[linker->symtab_sec_idx];
+
 		/* shdr->sh_link points to SYMTAB */
 		dst_sec->shdr->sh_link = linker->symtab_sec_idx;