commit-graph: check order while reading fanout chunk

We read the fanout chunk, storing a pointer to it, but only confirm that
the entries are monotonic in a final "lite" verification step. Let's
move that into the actual OIDF chunk callback, so that we can report
problems immediately (for all the reasons given in the previous
"commit-graph: abort as soon as we see a bogus chunk" commit).

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

commit-graph.c

@@ -277,8 +277,6 @@ struct commit_graph *load_commit_graph_one_fd_st(struct repository *r,
 
 static int verify_commit_graph_lite(struct commit_graph *g)
 {
-	int i;
-
 	/*
 	 * Basic validation shared between parse_commit_graph()
 	 * which'll be called every time the graph is used, and the
@@ -291,27 +289,30 @@ static int verify_commit_graph_lite(struct commit_graph *g)
 	 * over g->num_commits, or runs a checksum on the commit-graph
 	 * itself.
 	 */
-	for (i = 0; i < 255; i++) {
-		uint32_t oid_fanout1 = ntohl(g->chunk_oid_fanout[i]);
-		uint32_t oid_fanout2 = ntohl(g->chunk_oid_fanout[i + 1]);
-
-		if (oid_fanout1 > oid_fanout2) {
-			error("commit-graph fanout values out of order");
-			return 1;
-		}
-	}
-
 	return 0;
 }
 
 static int graph_read_oid_fanout(const unsigned char *chunk_start,
 				 size_t chunk_size, void *data)
 {
 	struct commit_graph *g = data;
+	int i;
+
 	if (chunk_size != 256 * sizeof(uint32_t))
 		return error("commit-graph oid fanout chunk is wrong size");
 	g->chunk_oid_fanout = (const uint32_t *)chunk_start;
 	g->num_commits = ntohl(g->chunk_oid_fanout[255]);
+
+	for (i = 0; i < 255; i++) {
+		uint32_t oid_fanout1 = ntohl(g->chunk_oid_fanout[i]);
+		uint32_t oid_fanout2 = ntohl(g->chunk_oid_fanout[i + 1]);
+
+		if (oid_fanout1 > oid_fanout2) {
+			error("commit-graph fanout values out of order");
+			return 1;
+		}
+	}
+
 	return 0;
 }
 

t/t5318-commit-graph.sh

@@ -867,6 +867,7 @@ test_expect_success 'reader notices out-of-bounds fanout' '
 	check_corrupt_chunk OIDF 0 $(printf "%02x000000" $(test_seq 0 254)) &&
 	cat >expect.err <<-\EOF &&
 	error: commit-graph fanout values out of order
+	error: commit-graph required OID fanout chunk missing or corrupted
 	EOF
 	test_cmp expect.err err
 '