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>

1 files changed, 8 insertions, 0 deletions

diff --git a/tree.c b/tree.c
index 62fed632d..1cbf60ea2 100644
--- a/tree.c
+++ b/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);