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clear parsed flag when we free tree buffers

Many code paths will free a tree object's buffer and set it
to NULL after finishing with it in order to keep memory
usage down during a traversal. However, out of 8 sites that
do this, only one actually unsets the "parsed" flag back.
Those sites that don't are setting a trap for later users of
the tree object; even after calling parse_tree, the buffer
will remain NULL, causing potential segfaults.

It is not known whether this is triggerable in the current
code. Most commands do not do an in-memory traversal
followed by actually using the objects again. However, it
does not hurt to be safe for future callers.

In most cases, we can abstract this out to a
"free_tree_buffer" helper. However, there are two
exceptions:

  1. The fsck code relies on the parsed flag to know that we
     were able to parse the object at one point. We can
     switch this to using a flag in the "flags" field.

  2. The index-pack code sets the buffer to NULL but does
     not free it (it is freed by a caller). We should still
     unset the parsed flag here, but we cannot use our
     helper, as we do not want to free the buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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1 parent edca415 commit 6e454b9a31840102807f1eee527ee717bf134102 @peff peff committed with gitster Jun 5, 2013
Showing with 24 additions and 23 deletions.
  1. +8 −9 builtin/fsck.c
  2. +1 −0 builtin/index-pack.c
  3. +1 −2 builtin/reflog.c
  4. +1 −2 http-push.c
  5. +1 −2 list-objects.c
  6. +1 −2 reachable.c
  7. +1 −2 revision.c
  8. +8 −0 tree.c
  9. +1 −0 tree.h
  10. +1 −4 walker.c
View
17 builtin/fsck.c
@@ -16,6 +16,7 @@
#define REACHABLE 0x0001
#define SEEN 0x0002
+#define HAS_OBJ 0x0004
static int show_root;
static int show_tags;
@@ -101,7 +102,7 @@ static int mark_object(struct object *obj, int type, void *data)
if (obj->flags & REACHABLE)
return 0;
obj->flags |= REACHABLE;
- if (!obj->parsed) {
+ if (!(obj->flags & HAS_OBJ)) {
if (parent && !has_sha1_file(obj->sha1)) {
printf("broken link from %7s %s\n",
typename(parent->type), sha1_to_hex(parent->sha1));
@@ -127,16 +128,13 @@ static int traverse_one_object(struct object *obj)
struct tree *tree = NULL;
if (obj->type == OBJ_TREE) {
- obj->parsed = 0;
tree = (struct tree *)obj;
if (parse_tree(tree) < 0)
return 1; /* error already displayed */
}
result = fsck_walk(obj, mark_object, obj);
- if (tree) {
- free(tree->buffer);
- tree->buffer = NULL;
- }
+ if (tree)
+ free_tree_buffer(tree);
return result;
}
@@ -178,7 +176,7 @@ static void check_reachable_object(struct object *obj)
* except if it was in a pack-file and we didn't
* do a full fsck
*/
- if (!obj->parsed) {
+ if (!(obj->flags & HAS_OBJ)) {
if (has_sha1_pack(obj->sha1))
return; /* it is in pack - forget about it */
printf("missing %s %s\n", typename(obj->type), sha1_to_hex(obj->sha1));
@@ -306,8 +304,7 @@ static int fsck_obj(struct object *obj)
if (obj->type == OBJ_TREE) {
struct tree *item = (struct tree *) obj;
- free(item->buffer);
- item->buffer = NULL;
+ free_tree_buffer(item);
}
if (obj->type == OBJ_COMMIT) {
@@ -340,6 +337,7 @@ static int fsck_sha1(const unsigned char *sha1)
return error("%s: object corrupt or missing",
sha1_to_hex(sha1));
}
+ obj->flags |= HAS_OBJ;
return fsck_obj(obj);
}
@@ -352,6 +350,7 @@ static int fsck_obj_buffer(const unsigned char *sha1, enum object_type type,
errors_found |= ERROR_OBJECT;
return error("%s: object corrupt or missing", sha1_to_hex(sha1));
}
+ obj->flags = HAS_OBJ;
return fsck_obj(obj);
}
View
1 builtin/index-pack.c
@@ -765,6 +765,7 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
if (obj->type == OBJ_TREE) {
struct tree *item = (struct tree *) obj;
item->buffer = NULL;
+ obj->parsed = 0;
}
if (obj->type == OBJ_COMMIT) {
struct commit *commit = (struct commit *) obj;
View
3 builtin/reflog.c
@@ -94,8 +94,7 @@ static int tree_is_complete(const unsigned char *sha1)
complete = 0;
}
}
- free(tree->buffer);
- tree->buffer = NULL;
+ free_tree_buffer(tree);
if (complete)
tree->object.flags |= SEEN;
View
3 http-push.c
@@ -1330,8 +1330,7 @@ static struct object_list **process_tree(struct tree *tree,
break;
}
- free(tree->buffer);
- tree->buffer = NULL;
+ free_tree_buffer(tree);
return p;
}
View
3 list-objects.c
@@ -123,8 +123,7 @@ static void process_tree(struct rev_info *revs,
cb_data);
}
strbuf_setlen(base, baselen);
- free(tree->buffer);
- tree->buffer = NULL;
+ free_tree_buffer(tree);
}
static void mark_edge_parents_uninteresting(struct commit *commit,
View
3 reachable.c
@@ -80,8 +80,7 @@ static void process_tree(struct tree *tree,
else
process_blob(lookup_blob(entry.sha1), p, &me, entry.path, cp);
}
- free(tree->buffer);
- tree->buffer = NULL;
+ free_tree_buffer(tree);
}
static void process_tag(struct tag *tag, struct object_array *p,
View
3 revision.c
@@ -134,8 +134,7 @@ void mark_tree_uninteresting(struct tree *tree)
* We don't care about the tree any more
* after it has been marked uninteresting.
*/
- free(tree->buffer);
- tree->buffer = NULL;
+ free_tree_buffer(tree);
}
void mark_parents_uninteresting(struct commit *commit)
View
8 tree.c
@@ -225,6 +225,14 @@ int parse_tree(struct tree *item)
return parse_tree_buffer(item, buffer, size);
}
+void free_tree_buffer(struct tree *tree)
+{
+ free(tree->buffer);
+ tree->buffer = NULL;
+ tree->size = 0;
+ tree->object.parsed = 0;
+}
+
struct tree *parse_tree_indirect(const unsigned char *sha1)
{
struct object *obj = parse_object(sha1);
View
1 tree.h
@@ -16,6 +16,7 @@ struct tree *lookup_tree(const unsigned char *sha1);
int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size);
int parse_tree(struct tree *tree);
+void free_tree_buffer(struct tree *tree);
/* Parses and returns the tree in the given ent, chasing tags and commits. */
struct tree *parse_tree_indirect(const unsigned char *sha1);
View
5 walker.c
@@ -56,10 +56,7 @@ static int process_tree(struct walker *walker, struct tree *tree)
if (!obj || process(walker, obj))
return -1;
}
- free(tree->buffer);
- tree->buffer = NULL;
- tree->size = 0;
- tree->object.parsed = 0;
+ free_tree_buffer(tree);
return 0;
}

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