[PATCH 01/23] parse_commit_buffer(): treat lookup_commit() failure as parse error

From: Jeff King <peff@peff.net>
Date: Oct 18, 2019, 04:42 UTC
Message-ID: <20191018044212.GA17879@sigill.intra.peff.net>
In-Reply-To: <20191018044103.GA17625@sigill.intra.peff.net>

While parsing the parents of a commit, if we are able to parse an actual oid but lookup_commit() fails on it (because we previously saw it in this process as a different object type), we silently omit the parent and do not report any error to the caller.

The caller has no way of knowing this happened, because even an empty parent list is a valid parse result. As a result, it's possible to fool our "rev-list" connectivity check into accepting a corrupted set of objects.

There's a test for this case already in t6102, but unfortunately it has a slight error. It creates a broken commit with a parent line pointing to a blob, and then checks that rev-list notices the problem in two cases:

  1. the "lone" case: we traverse the broken commit by itself (here we
     try to actually load the blob from disk and find out that it's not
     a commit)

  2. the "seen" case: we parse the blob earlier in the process, and then
     when calling lookup_commit() we realize immediately that it's not a
     commit

The "seen" variant for this test mistakenly parsed another commit instead of the blob, meaning that we were actually just testing the "lone" case again. Changing that reveals the breakage (and shows that this fixes it).

Signed-off-by: Jeff King <peff@peff.net>
---
 commit.c                               | 11 ++++++++---
 t/t6102-rev-list-unexpected-objects.sh |  2 +-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/commit.c b/commit.c
index 40890ae7ce..6467c9e175 100644
--- a/commit.c
+++ b/commit.c
@@ -432,8 +432,11 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 		if (graft && (graft->nr_parent < 0 || grafts_replace_parents))
 			continue;
 		new_parent = lookup_commit(r, &parent);
-		if (new_parent)
-			pptr = &commit_list_insert(new_parent, pptr)->next;
+		if (!new_parent)
+			return error("bad parent %s in commit %s",
+				     oid_to_hex(&parent),
+				     oid_to_hex(&item->object.oid));
+		pptr = &commit_list_insert(new_parent, pptr)->next;
 	}
 	if (graft) {
 		int i;
@@ -442,7 +445,9 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 			new_parent = lookup_commit(r,
 						   &graft->parent[i]);
 			if (!new_parent)
-				continue;
+				return error("bad graft parent %s in commit %s",
+					     oid_to_hex(&graft->parent[i]),
+					     oid_to_hex(&item->object.oid));
 			pptr = &commit_list_insert(new_parent, pptr)->next;
 		}
 	}
diff --git a/t/t6102-rev-list-unexpected-objects.sh b/t/t6102-rev-list-unexpected-objects.sh
index 28611c978e..52cde097dd 100755
--- a/t/t6102-rev-list-unexpected-objects.sh
+++ b/t/t6102-rev-list-unexpected-objects.sh
@@ -52,7 +52,7 @@ test_expect_success 'traverse unexpected non-commit parent (lone)' '
 '
 
 test_expect_success 'traverse unexpected non-commit parent (seen)' '
-	test_must_fail git rev-list --objects $commit $broken_commit \
+	test_must_fail git rev-list --objects $blob $broken_commit \
 		>output 2>&1 &&
 	test_i18ngrep "not a commit" output
 '

-- 
2.23.0.1228.gee29b05929