[PATCH 2/2] userns: Add KUnit test suite for uid_gid_map

[Bill Wendling]

Add a KUnit test suite to verify the insertion and sorting of mappings
in struct uid_gid_map. This test suite validates both base extent
insertion (<= 5 mappings) and extended extent insertion (> 5 mappings,
which triggers the allocation of the forward and reverse pointers).

This is especially useful for verifying that the __counted_by_ptr
attribute added to 'forward' and 'reverse' pointers works correctly
without causing any runtime bounds-checking panics or traps.

Assisted-by: Gemini Next
Signed-off-by: Bill Wendling <morbo@xxxxxxxxxx>
---
v2 - Remove Gerrit tag.
---
Cc: Kees Cook <kees@xxxxxxxxxx>
Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Aleksa Sarai <cyphar@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Miguel Ojeda <ojeda@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
Cc: Nicolas Schier <nsc@xxxxxxxxxx>
Cc: Gary Guo <gary@xxxxxxxxxxx>
Cc: "Thomas Weißschuh" <thomas.weissschuh@xxxxxxxxxxxxx>
Cc: Alice Ryhl <aliceryhl@xxxxxxxxxx>
Cc: Douglas Anderson <dianders@xxxxxxxxxxxx>
Cc: Anand Moon <linux.amoon@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: codemender-patching+linux@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-hardening@xxxxxxxxxxxxxxx
---
 init/Kconfig                  | 10 ++++
 kernel/.kunitconfig           |  3 ++
 kernel/user_namespace.c       |  4 ++
 kernel/user_namespace_kunit.c | 87 +++++++++++++++++++++++++++++++++++
 4 files changed, 104 insertions(+)
 create mode 100644 kernel/.kunitconfig
 create mode 100644 kernel/user_namespace_kunit.c

diff --git a/init/Kconfig b/init/Kconfig
index f63bf5e05e79..ba6a40b7315a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1457,6 +1457,16 @@ config USER_NS
 
 	  If unsure, say N.
 
+config USER_NAMESPACE_KUNIT_TEST
+	tristate "KUnit test for user namespace map insertion" if !KUNIT_ALL_TESTS
+	depends on USER_NS && KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the KUnit test for user namespace uid/gid map insertion.
+	  It validates map insertion, limits, dynamic allocation of the
+	  extended extents array, and mapping sorting functions.
+	  If unsure, say N.
+
 config PID_NS
 	bool "PID Namespaces"
 	default y
diff --git a/kernel/.kunitconfig b/kernel/.kunitconfig
new file mode 100644
index 000000000000..7314dce05dc2
--- /dev/null
+++ b/kernel/.kunitconfig
@@ -0,0 +1,3 @@
+CONFIG_KUNIT=y
+CONFIG_USER_NS=y
+CONFIG_USER_NAMESPACE_KUNIT_TEST=y
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 7e5371d8f515..64c64e1028e8 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1413,3 +1413,7 @@ static __init int user_namespaces_init(void)
 	return 0;
 }
 subsys_initcall(user_namespaces_init);
+
+#if IS_ENABLED(CONFIG_USER_NAMESPACE_KUNIT_TEST)
+#include "user_namespace_kunit.c"
+#endif
diff --git a/kernel/user_namespace_kunit.c b/kernel/user_namespace_kunit.c
new file mode 100644
index 000000000000..6d7662ef1916
--- /dev/null
+++ b/kernel/user_namespace_kunit.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for user namespace map insertion and sorting.
+ */
+
+#include <kunit/test.h>
+#include <linux/user_namespace.h>
+
+static void test_user_ns_map_insert_base(struct kunit *test)
+{
+	struct uid_gid_map map;
+	struct uid_gid_extent extent;
+	int i, ret;
+
+	memset(&map, 0, sizeof(map));
+
+	/* Insert up to UID_GID_MAP_MAX_BASE_EXTENTS (5) elements */
+	for (i = 0; i < UID_GID_MAP_MAX_BASE_EXTENTS; i++) {
+		extent.first = i * 10;
+		extent.lower_first = i * 100;
+		extent.count = 5;
+
+		ret = insert_extent(&map, &extent);
+		KUNIT_EXPECT_EQ(test, ret, 0);
+		KUNIT_EXPECT_EQ(test, map.nr_extents, i + 1);
+		KUNIT_EXPECT_EQ(test, map.extent[i].first, i * 10);
+		KUNIT_EXPECT_EQ(test, map.extent[i].lower_first, i * 100);
+		KUNIT_EXPECT_EQ(test, map.extent[i].count, 5);
+	}
+}
+
+static void test_user_ns_map_insert_extended(struct kunit *test)
+{
+	struct uid_gid_map map;
+	struct uid_gid_extent extent;
+	int i, ret;
+
+	memset(&map, 0, sizeof(map));
+
+	/* Insert more than UID_GID_MAP_MAX_BASE_EXTENTS (e.g., 10) elements */
+	for (i = 0; i < 10; i++) {
+		extent.first = i * 10;
+		extent.lower_first = i * 100;
+		extent.count = 5;
+
+		ret = insert_extent(&map, &extent);
+		KUNIT_EXPECT_EQ(test, ret, 0);
+		KUNIT_EXPECT_EQ(test, map.nr_extents, i + 1);
+
+		if (i < UID_GID_MAP_MAX_BASE_EXTENTS) {
+			KUNIT_EXPECT_EQ(test, map.extent[i].first, i * 10);
+		} else {
+			KUNIT_EXPECT_NOT_ERR_OR_NULL(test, map.forward);
+			KUNIT_EXPECT_EQ(test, map.forward[i].first, i * 10);
+			KUNIT_EXPECT_EQ(test, map.forward[i].lower_first, i * 100);
+			KUNIT_EXPECT_EQ(test, map.forward[i].count, 5);
+		}
+	}
+
+	/* Now sort the map to set up reverse mapping */
+	ret = sort_idmaps(&map);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_NOT_ERR_OR_NULL(test, map.reverse);
+
+	/* Verify sorting is correct */
+	for (i = 0; i < map.nr_extents; i++) {
+		KUNIT_EXPECT_EQ(test, map.forward[i].count, 5);
+		KUNIT_EXPECT_EQ(test, map.reverse[i].count, 5);
+	}
+
+	/* Clean up allocations to avoid leaks */
+	kfree(map.forward);
+	kfree(map.reverse);
+}
+
+static struct kunit_case user_ns_map_test_cases[] = {
+	KUNIT_CASE(test_user_ns_map_insert_base),
+	KUNIT_CASE(test_user_ns_map_insert_extended),
+	{}
+};
+
+static struct kunit_suite user_ns_map_test_suite = {
+	.name = "user_ns_map",
+	.test_cases = user_ns_map_test_cases,
+};
+
+kunit_test_suite(user_ns_map_test_suite);
-- 
2.55.0.860.g4b6b3295ed-goog