Subject: [PATCH v2] reflog-walk: don't segfault on non-commit sha1's in the reflog

From: Dennis Kaarsemaker <[email-masked]>
Date: Wed, 30 Dec 2015 23:17:08 +0100

Use lookup_commit instead of parse_object to look up commits mentioned
in the reflog. This avoids a segfault in save_parents if somehow a sha1
for something other than a commit ends up in the reflog.

Signed-off-by: Dennis Kaarsemaker <[email-masked]>
Helped-by: Nguyễn Thái Ngọc Duy <[email-masked]>
Helped-by: Junio C Hamano <[email-masked]>
---
 reflog-walk.c     |  7 +++++--
 t/t1410-reflog.sh | 13 +++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

This version implements Junio's way of doing this, to avoid spurious warnings
and to handle broken commit objects better.

I also added a failing test to show that git reflog still fails to display the
full reflog when it encounters such non-commit objects (it just stops when it
seems them). I don't know how to fix that.

The really correct way of fixing this bug may actually be a level higher, and
making git reflog not rely on information about parent commits, whether they
are fake or not.

diff --git a/reflog-walk.c b/reflog-walk.c
index 85b8a54..861d7c4 100644
--- a/reflog-walk.c
+++ b/reflog-walk.c
@@ -221,6 +221,7 @@ void fake_reflog_parent(struct reflog_walk_info *info, struct commit *commit)
 	struct commit_info *commit_info =
 		get_commit_info(commit, &info->reflogs, 0);
 	struct commit_reflog *commit_reflog;
+	struct object *logobj;
 	struct reflog_info *reflog;
 
 	info->last_commit_reflog = NULL;
@@ -236,11 +237,13 @@ void fake_reflog_parent(struct reflog_walk_info *info, struct commit *commit)
 	reflog = &commit_reflog->reflogs->items[commit_reflog->recno];
 	info->last_commit_reflog = commit_reflog;
 	commit_reflog->recno--;
-	commit_info->commit = (struct commit *)parse_object(reflog->osha1);
-	if (!commit_info->commit) {
+	logobj = parse_object(reflog->osha1);
+	if (!logobj || logobj->type != OBJ_COMMIT) {
+		commit_info->commit = NULL;
 		commit->parents = NULL;
 		return;
 	}
+	commit_info->commit = (struct commit *)logobj;
 
 	commit->parents = xcalloc(1, sizeof(struct commit_list));
 	commit->parents->item = commit_info->commit;
diff --git a/t/t1410-reflog.sh b/t/t1410-reflog.sh
index b79049f..130d671 100755
--- a/t/t1410-reflog.sh
+++ b/t/t1410-reflog.sh
@@ -325,4 +325,17 @@ test_expect_success 'parsing reverse reflogs at BUFSIZ boundaries' '
 	test_cmp expect actual
 '
 
+test_expect_success 'no segfaults for reflog containing non-commit sha1s' '
+	git update-ref --create-reflog -m "Creating ref" \
+		refs/tests/tree-in-reflog HEAD &&
+	git update-ref -m "Forcing tree" refs/tests/tree-in-reflog HEAD^{tree} &&
+	git update-ref -m "Restoring to commit" refs/tests/tree-in-reflog HEAD &&
+	git reflog refs/tests/tree-in-reflog
+'
+
+test_expect_failure 'reflog containing non-commit sha1s displays fully' '
+	git reflog refs/tests/tree-in-reflog > actual &&
+	test_line_count = 3 actual
+'
+
 test_done
-- 
2.7.0-rc1-207-ga35084c