[PATCH dwarves] dwarf_loader: Fix heap overflow when accessing variable specification

[Ilya Leoshkevich <iii@linux.ibm.com>]

Variables can be allocated with or without specification, however,
tag__recode_dwarf_type() always tries accessing it, leading to heap
read overflows and subsequent logic bugs.

Fix by introducing a bit that tracks whether or not specification is
present.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 dwarf_loader.c | 15 ++++++++++-----
 dwarves.h      |  1 +
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/dwarf_loader.c b/dwarf_loader.c
index 48e1bf0..60bdca3 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -723,6 +723,7 @@ static struct variable *variable__new(Dwarf_Die *die, struct cu *cu, struct conf
 		var->external = dwarf_hasattr(die, DW_AT_external);
 		/* non-defining declaration of an object */
 		var->declaration = dwarf_hasattr(die, DW_AT_declaration);
+		var->has_specification = has_specification;
 		var->scope = VSCOPE_UNKNOWN;
 		INIT_LIST_HEAD(&var->annots);
 		var->ip.addr = 0;
@@ -2291,12 +2292,16 @@ static int tag__recode_dwarf_type(struct tag *tag, struct cu *cu)
 		goto find_type;
 	case DW_TAG_variable: {
 		struct variable *var = tag__variable(tag);
-		dwarf_off_ref specification = dwarf_tag__spec(dtag);
 
-		if (specification.off) {
-			dtype = dwarf_cu__find_tag_by_ref(cu->priv, &specification);
-			if (dtype)
-				var->spec = tag__variable(dtype->tag);
+		if (var->has_specification) {
+			dwarf_off_ref specification = dwarf_tag__spec(dtag);
+
+			if (specification.off) {
+				dtype = dwarf_cu__find_tag_by_ref(cu->priv,
+								  &specification);
+				if (dtype)
+					var->spec = tag__variable(dtype->tag);
+			}
 		}
 	}
 
diff --git a/dwarves.h b/dwarves.h
index 30d33fa..20608dd 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -691,6 +691,7 @@ struct variable {
 	const char	 *name;
 	uint8_t		 external:1;
 	uint8_t		 declaration:1;
+	uint8_t		 has_specification:1;
 	enum vscope	 scope;
 	struct location	 location;
 	struct hlist_node tool_hnode;
-- 
2.31.1