multi-pack-index: verify oid fanout order

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

midx.c

@@ -950,5 +950,14 @@ int verify_midx_file(const char *object_dir)
 			midx_report("failed to load pack in position %d", i);
 	}
 
+	for (i = 0; i < 255; i++) {
+		uint32_t oid_fanout1 = ntohl(m->chunk_oid_fanout[i]);
+		uint32_t oid_fanout2 = ntohl(m->chunk_oid_fanout[i + 1]);
+
+		if (oid_fanout1 > oid_fanout2)
+			midx_report(_("oid fanout out of order: fanout[%d] = %"PRIx32" > %"PRIx32" = fanout[%d]"),
+				    i, oid_fanout1, oid_fanout2, i + 1);
+	}
+
 	return verify_midx_error;
 }

t/t5319-multi-pack-index.sh

@@ -186,6 +186,9 @@ MIDX_CHUNK_LOOKUP_WIDTH=12
 MIDX_OFFSET_PACKNAMES=$(($MIDX_HEADER_SIZE + \
 			 $MIDX_NUM_CHUNKS * $MIDX_CHUNK_LOOKUP_WIDTH))
 MIDX_BYTE_PACKNAME_ORDER=$(($MIDX_OFFSET_PACKNAMES + 2))
+MIDX_OFFSET_OID_FANOUT=$(($MIDX_OFFSET_PACKNAMES + 652))
+MIDX_OID_FANOUT_WIDTH=4
+MIDX_BYTE_OID_FANOUT_ORDER=$((MIDX_OFFSET_OID_FANOUT + 250 * $MIDX_OID_FANOUT_WIDTH + 1))
 
 test_expect_success 'verify bad version' '
 	corrupt_midx_and_verify $MIDX_BYTE_VERSION "\00" $objdir \
@@ -227,6 +230,11 @@ test_expect_success 'verify packnames out of order' '
 		"failed to load pack"
 '
 
+test_expect_success 'verify oid fanout out of order' '
+	corrupt_midx_and_verify $MIDX_BYTE_OID_FANOUT_ORDER "\01" $objdir \
+		"oid fanout out of order"
+'
+
 test_expect_success 'repack removes multi-pack-index' '
 	test_path_is_file $objdir/pack/multi-pack-index &&
 	git repack -adf &&