[PATCH v3 4/8] reftable: ensure tables in a stack use sequential update indices

From

Karthik Nayak <karthik.188@gmail.com>

Date

Sep 18, 2025, 08:11 UTC

Message-ID

<20250918-228-reftable-introduce-consistency-checks-v3-4-271af03eb34d@gmail.com>

In-Reply-To

<20250918-228-reftable-introduce-consistency-checks-v3-0-271af03eb34d@gmail.com>

Raise a 'REFTABLE_FORMAT_ERROR' when this validation fails.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 reftable/stack.c                |  9 +++++++++
 t/unit-tests/u-reftable-stack.c | 28 ++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/reftable/stack.c b/reftable/stack.c
index 955be1edb6..a458f5a4c5 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -238,6 +238,7 @@ static int reftable_stack_reload_once(struct reftable_stack *st,
 				      int reuse_open)
 {
 	size_t cur_len = !st->merged ? 0 : st->merged->tables_len;
+	const struct reftable_table *prev_table = NULL;
 	struct reftable_table **cur = NULL;
 	struct reftable_table **reused = NULL;
 	struct reftable_table **new_tables = NULL;
@@ -317,6 +318,14 @@ static int reftable_stack_reload_once(struct reftable_stack *st,
 
 		new_tables[new_tables_len] = table;
 		new_tables_len++;
+
+		/* table's update indices must be sequential */
+		if (prev_table && (prev_table->max_update_index != table->min_update_index - 1)) {
+			err = REFTABLE_FORMAT_ERROR;
+			goto done;
+		}
+
+		prev_table = table;
 	}
 
 	/* success! */
diff --git a/t/unit-tests/u-reftable-stack.c b/t/unit-tests/u-reftable-stack.c
index a8b91812e8..465f4a2689 100644
--- a/t/unit-tests/u-reftable-stack.c
+++ b/t/unit-tests/u-reftable-stack.c
@@ -1330,3 +1330,31 @@ void test_reftable_stack__invalid_limit_updates(void)
 	reftable_stack_destroy(st);
 	clear_dir(dir);
 }
+
+void test_reftable_stack__non_seq_update_indices(void)
+{
+	struct reftable_write_options opts = { 0 };
+	struct reftable_stack *st1 = NULL;
+	char *dir = get_tmp_dir(__LINE__);
+
+	struct reftable_ref_record ref1 = {
+		.refname = (char *)"HEAD",
+		.update_index = 1,
+		.value_type = REFTABLE_REF_SYMREF,
+		.value.symref = (char *)"master",
+	};
+	struct reftable_ref_record ref2 = {
+		.refname = (char *)"branch2",
+		.update_index = 3,
+		.value_type = REFTABLE_REF_SYMREF,
+		.value.symref = (char *)"master",
+	};
+
+	cl_assert_equal_i(reftable_new_stack(&st1, dir, &opts), 0);
+	cl_assert_equal_i(reftable_stack_add(st1, write_test_ref, &ref1, 0), 0);
+	cl_assert_equal_i(reftable_stack_add(st1, write_test_ref, &ref2, 0),
+			  REFTABLE_FORMAT_ERROR);
+
+	reftable_stack_destroy(st1);
+	clear_dir(dir);
+}

-- 
2.51.0