[PATCH 2/2] selftests/namespaces: add uid_map/gid_map range tests

[Natasha Klaus]

Check that a uid_map or gid_map line with a value that does not fit in
u32 is rejected with EINVAL and installs nothing, for each of the three
fields, and that an in-range line is still accepted and reads back
unchanged.

Signed-off-by: Natasha Klaus <natalie.klaus@xxxxxxxxxxxxxxxxxxxxxxx>
Assisted-by: LLM
---
 tools/testing/selftests/namespaces/.gitignore |   1 +
 tools/testing/selftests/namespaces/Makefile   |   3 +-
 .../selftests/namespaces/uid_map_range_test.c | 155 ++++++++++++++++++
 3 files changed, 158 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/namespaces/uid_map_range_test.c

diff --git a/tools/testing/selftests/namespaces/.gitignore b/tools/testing/selftests/namespaces/.gitignore
index 0989e80da457..995b082357fa 100644
--- a/tools/testing/selftests/namespaces/.gitignore
+++ b/tools/testing/selftests/namespaces/.gitignore
@@ -10,3 +10,4 @@ cred_change_test
 stress_test
 listns_pagination_bug
 regression_pidfd_setns_test
+uid_map_range_test
diff --git a/tools/testing/selftests/namespaces/Makefile b/tools/testing/selftests/namespaces/Makefile
index fbb821652c17..9b22d12708e1 100644
--- a/tools/testing/selftests/namespaces/Makefile
+++ b/tools/testing/selftests/namespaces/Makefile
@@ -13,7 +13,8 @@ TEST_GEN_PROGS := nsid_test \
 		  cred_change_test \
 		  stress_test \
 		  listns_pagination_bug \
-		  regression_pidfd_setns_test
+		  regression_pidfd_setns_test \
+		  uid_map_range_test
 
 include ../lib.mk
 
diff --git a/tools/testing/selftests/namespaces/uid_map_range_test.c b/tools/testing/selftests/namespaces/uid_map_range_test.c
new file mode 100644
index 000000000000..9da02005a09c
--- /dev/null
+++ b/tools/testing/selftests/namespaces/uid_map_range_test.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include "../kselftest_harness.h"
+
+/*
+ * The fields of a uid_map/gid_map line are stored in u32. Values that
+ * do not fit must be rejected with EINVAL instead of being silently
+ * truncated modulo 2^32, and in-range values must still be accepted.
+ */
+
+static int write_file(const char *path, const char *buf)
+{
+	ssize_t len = strlen(buf);
+	ssize_t ret;
+	int fd;
+
+	fd = open(path, O_WRONLY | O_CLOEXEC);
+	if (fd < 0)
+		return -errno;
+	ret = write(fd, buf, len);
+	if (ret < 0)
+		ret = -errno;
+	close(fd);
+	if (ret < 0)
+		return ret;
+	return ret == len ? 0 : -EIO;
+}
+
+static ssize_t read_file(const char *path, char *buf, size_t size)
+{
+	ssize_t ret;
+	int fd;
+
+	fd = open(path, O_RDONLY | O_CLOEXEC);
+	if (fd < 0)
+		return -errno;
+	ret = read(fd, buf, size - 1);
+	if (ret < 0)
+		ret = -errno;
+	else
+		buf[ret] = '\0';
+	close(fd);
+	return ret;
+}
+
+/* Enter a fresh user namespace, remembering the outer ids. */
+static int enter_userns(uid_t *uid, gid_t *gid)
+{
+	*uid = geteuid();
+	*gid = getegid();
+	if (unshare(CLONE_NEWUSER) < 0)
+		return -errno;
+	/* Required before an unprivileged gid_map write. */
+	return write_file("/proc/self/setgroups", "deny");
+}
+
+static void expect_rejected(struct __test_metadata *_metadata,
+			    const char *path, const char *line)
+{
+	char buf[256];
+
+	TH_LOG("writing \"%s\" to %s", line, path);
+	EXPECT_EQ(write_file(path, line), -EINVAL);
+	/* Nothing may have been installed. */
+	EXPECT_EQ(read_file(path, buf, sizeof(buf)), 0) {
+		TH_LOG("installed: %s", buf);
+	}
+}
+
+TEST(uid_map_first_above_u32)
+{
+	char line[64];
+	uid_t uid;
+	gid_t gid;
+	int ret;
+
+	ret = enter_userns(&uid, &gid);
+	if (ret)
+		SKIP(return, "cannot set up user namespace: %s", strerror(-ret));
+	snprintf(line, sizeof(line), "4294967301 %u 1", uid);
+	expect_rejected(_metadata, "/proc/self/uid_map", line);
+}
+
+TEST(uid_map_lower_first_above_u32)
+{
+	char line[64];
+	uid_t uid;
+	gid_t gid;
+	int ret;
+
+	ret = enter_userns(&uid, &gid);
+	if (ret)
+		SKIP(return, "cannot set up user namespace: %s", strerror(-ret));
+	snprintf(line, sizeof(line), "0 %llu 1", (1ULL << 32) + uid);
+	expect_rejected(_metadata, "/proc/self/uid_map", line);
+}
+
+TEST(uid_map_count_above_u32)
+{
+	char line[64];
+	uid_t uid;
+	gid_t gid;
+	int ret;
+
+	ret = enter_userns(&uid, &gid);
+	if (ret)
+		SKIP(return, "cannot set up user namespace: %s", strerror(-ret));
+	snprintf(line, sizeof(line), "0 %u 4294967297", uid);
+	expect_rejected(_metadata, "/proc/self/uid_map", line);
+}
+
+TEST(gid_map_first_above_u32)
+{
+	char line[64];
+	uid_t uid;
+	gid_t gid;
+	int ret;
+
+	ret = enter_userns(&uid, &gid);
+	if (ret)
+		SKIP(return, "cannot set up user namespace: %s", strerror(-ret));
+	snprintf(line, sizeof(line), "4294967301 %u 1", gid);
+	expect_rejected(_metadata, "/proc/self/gid_map", line);
+}
+
+TEST(uid_map_in_range)
+{
+	unsigned int first, lower_first, count;
+	char line[64], buf[256];
+	uid_t uid;
+	gid_t gid;
+	int ret;
+
+	ret = enter_userns(&uid, &gid);
+	if (ret)
+		SKIP(return, "cannot set up user namespace: %s", strerror(-ret));
+	snprintf(line, sizeof(line), "5 %u 1", uid);
+	ASSERT_EQ(write_file("/proc/self/uid_map", line), 0);
+
+	ASSERT_GT(read_file("/proc/self/uid_map", buf, sizeof(buf)), 0);
+	ASSERT_EQ(sscanf(buf, "%u %u %u", &first, &lower_first, &count), 3);
+	EXPECT_EQ(first, 5U);
+	EXPECT_EQ(lower_first, uid);
+	EXPECT_EQ(count, 1U);
+	/* Exactly one extent. */
+	EXPECT_EQ(strchr(buf, '\n'), buf + strlen(buf) - 1);
+}
+
+TEST_HARNESS_MAIN
-- 
2.34.1