Re: [PATCH v4 2/2] userns: Add KUnit test suite for uid_gid_map

[Thomas Weißschuh]

On Wed, Aug 26, 2026 at 10:00:35PM +0000, Bill Wendling wrote:
> 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:3.1-pro-preview
> Signed-off-by: Bill Wendling <morbo@xxxxxxxxxx>
> ---
> v2 - Remove Gerrit tag.
> v3 - s/KUNIT_EXPECT_NOT_ERR_OR_NULL/KUNIT_ASSERT_NOT_ERR_OR_NULL/
>    - Fixed Kconfig tests.
> v4 - Actually test on unsorted data. Corrected the "Assisted-by" tag.
> ---
> Cc: Bradley Morgan <brads@xxxxxxxxxxxxxx>
> Cc: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> 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 | 92 +++++++++++++++++++++++++++++++++++
>  4 files changed, 109 insertions(+)
>  create mode 100644 kernel/.kunitconfig
>  create mode 100644 kernel/user_namespace_kunit.c
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index f63bf5e05e79..d460344539a5 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1457,6 +1457,16 @@ config USER_NS
>  
>  	  If unsure, say N.
>  
> +config USER_NAMESPACE_KUNIT_TEST
> +	bool "Test user namespace map insertion" if !KUNIT_ALL_TESTS
> +	depends on KUNIT=y

Urgh.

> +	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 786dbf0506ca..0e7373085af9 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -1417,3 +1417,7 @@ 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..88467361efdf
> --- /dev/null
> +++ b/kernel/user_namespace_kunit.c
> @@ -0,0 +1,92 @@
> +// 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_ASSERT_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);
> +	}
> +}

The extended test below already tests everything the 'base' one does.
Do we need both?

> +
> +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 */

When UID_GID_MAP_MAX_BASE_EXTENTS is ever increased, this might not be true anymore.
Add an assertion or make the iteration count dynamic.

> +	for (i = 0; i < 10; 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, i + 1);
> +
> +		if (i < UID_GID_MAP_MAX_BASE_EXTENTS) {
> +			KUNIT_EXPECT_EQ(test, map.extent[i].first, value * 10);
> +		} else {
> +			KUNIT_EXPECT_EQ(test, map.forward[i].first, value * 10);
> +			KUNIT_EXPECT_EQ(test, map.forward[i].lower_first, value  * 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_ASSERT_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].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);
> +	}

Isn't this the same as the original order?

> +
> +	kfree(map.forward);
> +	kfree(map.reverse);
> +}

(...)