[PATCH v4 15/21] object-file.c: guard against future bugs in loose_object_info()

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An earlier version of the preceding commit had a subtle bug where our
"type_scratch" (later assigned to "oi->typep") would be uninitialized
and used in the "!allow_unknown" case, at which point it would contain
a nonsensical value if we'd failed to call parse_loose_header().

The preceding commit introduced "parsed_header" variable to check for
this case, but I think we can do better, let's carry a "oi_header"
variable initially set to NULL, and only set it to "oi" once we're
past parse_loose_header().

This is functionally the same thing, but hopefully makes it even more
obvious in the future that we must not access the "typep" and
"sizep" (or "type_name") unless parse_loose_header() succeeds, but
that accessing other fields set earlier (such as the "disk_sizep" set
earlier) is OK.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
 object-file.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/object-file.c b/object-file.c
index 31263335af9..d41f444e6cc 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1393,7 +1393,7 @@ static int loose_object_info(struct repository *r,
 	struct strbuf hdrbuf = STRBUF_INIT;
 	unsigned long size_scratch;
 	enum object_type type_scratch;
-	int parsed_header = 0;
+	struct object_info *oi_header = NULL;
 	int allow_unknown = flags & OBJECT_INFO_ALLOW_UNKNOWN_TYPE;
 
 	if (oi->delta_base_oid)
@@ -1441,18 +1441,20 @@ static int loose_object_info(struct repository *r,
 		if (!parse_loose_header(hdrbuf.len ? hdrbuf.buf : hdr, oi))
 			/*
 			 * oi->{sizep,typep} are meaningless unless
-			 * parse_loose_header() returns >= 0.
+			 * parse_loose_header() returns >= 0. Let's
+			 * access them as "oi_header" (just an alias
+			 * for "oi") below to make that intent clear.
 			 */
-			parsed_header = 1;
+			oi_header = oi;
 		else
 			status = error(_("unable to parse %s header"), oid_to_hex(oid));
 	}
-	if (!allow_unknown && parsed_header && *oi->typep < 0)
+	if (!allow_unknown && oi_header && *oi_header->typep < 0)
 		die(_("invalid object type"));
 
-	if (parsed_header && oi->contentp) {
+	if (oi_header && oi->contentp) {
 		*oi->contentp = unpack_loose_rest(&stream, hdr,
-						  *oi->sizep, oid);
+						  *oi_header->sizep, oid);
 		if (!*oi->contentp) {
 			git_inflate_end(&stream);
 			status = -1;
-- 
2.32.0.606.g2e440ee2c94




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