userns: Add KUnit test suite for uid_gid_map

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.

Signed-off-by: Bill Wendling <morbo@google.com>
Link: https://patch.msgid.link/20260908222734.3048684-2-morbo@google.com
Tested-by: Bradley Morgan <brads@mainlining.org>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

6 files changed, 126 insertions, 2 deletions

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 2962256eddf7..633157781edc 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -207,6 +207,12 @@ extern bool in_userns(const struct user_namespace *ancestor,
 		       const struct user_namespace *child);
 extern bool current_in_userns(const struct user_namespace *target_ns);
 struct ns_common *ns_get_owner(struct ns_common *ns);
+
+#if IS_ENABLED(CONFIG_USER_NS_MAP_KUNIT_TEST)
+extern int insert_extent(struct uid_gid_map *map, struct uid_gid_extent *extent);
+extern int sort_idmaps(struct uid_gid_map *map);
+#endif /* CONFIG_USER_NS_MAP_KUNIT_TEST */
+
 #else
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
diff --git a/init/Kconfig b/init/Kconfig
index 8583d9f06c52..27c1ffc675bf 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1457,6 +1457,17 @@ config USER_NS
 
 	  If unsure, say N.
 
+config USER_NS_MAP_KUNIT_TEST
+	tristate "KUint 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/Makefile b/kernel/Makefile
index 1e1a31673577..2a64282749b8 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -141,6 +141,7 @@ obj-$(CONFIG_WATCH_QUEUE) += watch_queue.o
 
 obj-$(CONFIG_RESOURCE_KUNIT_TEST) += resource_kunit.o
 obj-$(CONFIG_SYSCTL_KUNIT_TEST) += sysctl-test.o
+obj-$(CONFIG_USER_NS_MAP_KUNIT_TEST) += tests/user_ns_map_kunit.o
 
 CFLAGS_kstack_erase.o += $(DISABLE_KSTACK_ERASE)
 CFLAGS_kstack_erase.o += $(call cc-option,-mgeneral-regs-only)
diff --git a/kernel/tests/.kunitconfig b/kernel/tests/.kunitconfig
new file mode 100644
index 000000000000..b3d1206fd81a
--- /dev/null
+++ b/kernel/tests/.kunitconfig
@@ -0,0 +1,4 @@
+CONFIG_KUNIT=y
+CONFIG_NAMESPACES=y
+CONFIG_USER_NS=y
+CONFIG_USER_NS_MAP_KUNIT_TEST=y
diff --git a/kernel/tests/user_ns_map_kunit.c b/kernel/tests/user_ns_map_kunit.c
new file mode 100644
index 000000000000..24c21e43a36c
--- /dev/null
+++ b/kernel/tests/user_ns_map_kunit.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for user namespace map insertion and sorting.
+ */
+
+#define pr_fmt(fmt) "user_namespace: " fmt
+
+#include <kunit/test.h>
+#include <linux/user_namespace.h>
+
+#define NR_EXTENTS (UID_GID_MAP_MAX_BASE_EXTENTS + 5)
+
+static void user_ns_map_insert(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 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_ASSERT_EQ(test, ret, 0);
+	}
+
+	KUNIT_EXPECT_EQ(test, map.nr_extents, UID_GID_MAP_MAX_BASE_EXTENTS);
+
+	/* Verify the elements ended up in the 'extent' array */
+	for (i = 0; i < UID_GID_MAP_MAX_BASE_EXTENTS; i++) {
+		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 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 elements */
+	for (i = 0; i < NR_EXTENTS; i++) {
+		int value = 9 - i;
+
+		extent.first = value * 10;
+		extent.lower_first = value * 100;
+		extent.count = 5;
+
+		ret = insert_extent(&map, &extent);
+		KUNIT_ASSERT_EQ(test, ret, 0);
+	}
+
+	KUNIT_EXPECT_EQ(test, map.nr_extents, NR_EXTENTS);
+
+	/* Now sort the map to set up reverse mapping */
+	ret = sort_idmaps(&map);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, map.reverse);
+
+	/* Verify the elements are in 'forward' and that sorting is correct */
+	for (i = 0; i < map.nr_extents; i++) {
+		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);
+
+		KUNIT_EXPECT_EQ(test, map.reverse[i].first, i * 10);
+		KUNIT_EXPECT_EQ(test, map.reverse[i].lower_first, i * 100);
+		KUNIT_EXPECT_EQ(test, map.reverse[i].count, 5);
+	}
+
+	kfree(map.forward);
+	kfree(map.reverse);
+}
+
+static struct kunit_case user_ns_map_test_cases[] = {
+	KUNIT_CASE(user_ns_map_insert),
+	KUNIT_CASE(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);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit test for user namespace map insertion");
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 7c8316c4271f..f9cbb4b92b48 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
+#include <kunit/visibility.h>
 #include <linux/export.h>
 #include <linux/nsproxy.h>
 #include <linux/slab.h>
@@ -783,7 +784,8 @@ static bool mappings_overlap(struct uid_gid_map *new_map,
  * Takes care to allocate a 4K block of memory if the number of mappings exceeds
  * UID_GID_MAP_MAX_BASE_EXTENTS.
  */
-static int insert_extent(struct uid_gid_map *map, struct uid_gid_extent *extent)
+VISIBLE_IF_KUNIT int insert_extent(struct uid_gid_map *map,
+				   struct uid_gid_extent *extent)
 {
 	struct uid_gid_extent *dest;
 
@@ -819,6 +821,7 @@ static int insert_extent(struct uid_gid_map *map, struct uid_gid_extent *extent)
 	*dest = *extent;
 	return 0;
 }
+EXPORT_SYMBOL_IF_KUNIT(insert_extent);
 
 /* cmp function to sort() forward mappings */
 static int cmp_extents_forward(const void *a, const void *b)
@@ -854,7 +857,7 @@ static int cmp_extents_reverse(const void *a, const void *b)
  * sort_idmaps - Sorts an array of idmap entries.
  * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
  */
-static int sort_idmaps(struct uid_gid_map *map)
+VISIBLE_IF_KUNIT int sort_idmaps(struct uid_gid_map *map)
 {
 	if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
 		return 0;
@@ -875,6 +878,7 @@ static int sort_idmaps(struct uid_gid_map *map)
 
 	return 0;
 }
+EXPORT_SYMBOL_IF_KUNIT(sort_idmaps);
 
 /**
  * verify_root_map() - check the uid 0 mapping