[PATCH v2 2/8] fs/acl: Add ACL mask interaction tests

Add acl_mask01 test with 3 test cases to validate ACL_MASK
interaction with named user and group entries:

1. ACL_USER with mask - Named user permissions restricted by mask
2. ACL_GROUP with mask - Named group permissions restricted by mask
3. ACL_GROUP_OBJ with mask - Group owner permissions restricted by mask

Each test verifies that:
- With mask set to rwx, access is granted
- With mask cleared (---), access is denied with EACCES

This validates that ACL_MASK correctly restricts permissions for
ACL_USER, ACL_GROUP, and ACL_GROUP_OBJ entries.

Signed-off-by: Sachin Sant <[email protected]>
---
V2 changes:
- Updated copyright header as per LTP format.
- v1 link https://lore.kernel.org/ltp/20260602121958.27494-1-sachinp-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org/T/#t

V1 changes:
- Use HAVE_LIBACL guards in .c code
- Report TCONF when libacl is not available
- rfc link https://lore.kernel.org/ltp/477836fd-80c8-4168-bfe6-00b374bb2534-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org/T/#t

---
 runtest/fs                           |   1 +
 testcases/kernel/fs/acl/.gitignore   |   1 +
 testcases/kernel/fs/acl/acl_mask01.c | 283 +++++++++++++++++++++++++++
 3 files changed, 285 insertions(+)
 create mode 100644 testcases/kernel/fs/acl/acl_mask01.c

diff --git a/runtest/fs b/runtest/fs
index 2a878744b..69ecb8647 100644
--- a/runtest/fs
+++ b/runtest/fs
@@ -90,3 +90,4 @@ squashfs01 squashfs01
 
 # Run the acl tests
 acl_user_obj01 acl_user_obj01
+acl_mask01 acl_mask01
diff --git a/testcases/kernel/fs/acl/.gitignore b/testcases/kernel/fs/acl/.gitignore
index d9c46db11..bfcdee93d 100644
--- a/testcases/kernel/fs/acl/.gitignore
+++ b/testcases/kernel/fs/acl/.gitignore
@@ -1 +1,2 @@
 /acl_user_obj01
+/acl_mask01
diff --git a/testcases/kernel/fs/acl/acl_mask01.c b/testcases/kernel/fs/acl/acl_mask01.c
new file mode 100644
index 000000000..4bf9324d4
--- /dev/null
+++ b/testcases/kernel/fs/acl/acl_mask01.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 IBM
+ *
+ * Original shell test by Kai Zhao ([email protected])
+ * Converted to C by Sachin Sant <[email protected]>
+ */
+
+/*\
+ * Test ACL mask interaction with named users and groups.
+ *
+ * Verify that ACL_MASK correctly restricts permissions for:
+ * - ACL_USER (named user) entries
+ * - ACL_GROUP (named group) entries
+ * - ACL_GROUP_OBJ (group owner) entries
+ *
+ * The mask acts as an upper bound on permissions for these entry types.
+ * Even if an entry grants full permissions, the mask can restrict them.
+ * ACL_USER_OBJ and ACL_OTHER are not affected by the mask.
+ *
+ * [Algorithm]
+ *
+ * For each entry type (ACL_USER, ACL_GROUP, ACL_GROUP_OBJ):
+ * 1. Set up ACL with full permissions for the entry
+ * 2. Set mask to allow full permissions (rwx)
+ * 3. Verify access is granted
+ * 4. Clear mask permissions (---)
+ * 5. Verify access is denied despite entry having full permissions
+ */
+
+#include "acl_lib.h"
+
+uid_t user1_uid, user2_uid, user3_uid;
+gid_t user1_gid, user2_gid, user3_gid;
+int users_created = 0;
+
+#ifdef HAVE_LIBACL
+
+/*
+ * Test ACL_USER permissions with mask.
+ * Named user permissions should be restricted by ACL_MASK.
+ */
+static void test_acl_user_with_mask(void)
+{
+	acl_t acl;
+	int err;
+
+	tst_res(TINFO, "Testing ACL_USER with mask");
+	reset_test_path();
+
+	acl = acl_init(5);
+	if (!acl)
+		tst_brk(TBROK | TERRNO, "acl_init failed");
+
+	add_acl_entry(acl, ACL_USER_OBJ,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_named_user_acl_entry(acl, user3_uid,
+				 ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_empty_acl_entry(acl, ACL_GROUP_OBJ);
+	add_acl_entry(acl, ACL_MASK,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_empty_acl_entry(acl, ACL_OTHER);
+
+	set_acl_file(TESTDIR, ACL_TYPE_ACCESS, acl);
+	safe_acl_free(acl);
+
+	err = try_create_as(user3_uid, user3_gid, 0644);
+	if (err) {
+		errno = err;
+		tst_res(TFAIL | TERRNO,
+			"ACL_USER with mask rwx should allow access");
+		return;
+	}
+
+	cleanup_testfile();
+
+	acl = acl_get_file(TESTDIR, ACL_TYPE_ACCESS);
+	if (!acl)
+		tst_brk(TBROK | TERRNO, "acl_get_file failed");
+
+	clear_acl_mask_perms(acl);
+	set_acl_file(TESTDIR, ACL_TYPE_ACCESS, acl);
+	safe_acl_free(acl);
+
+	err = try_create_as(user3_uid, user3_gid, 0644);
+	if (!err) {
+		cleanup_testfile();
+		tst_res(TFAIL, "ACL_USER with mask --- should deny access");
+		return;
+	}
+
+	if (err != EACCES) {
+		errno = err;
+		tst_res(TFAIL | TERRNO, "Expected EACCES from named user");
+		return;
+	}
+
+	tst_res(TPASS, "ACL_USER with mask works correctly");
+}
+
+/*
+ * Test ACL_GROUP permissions with mask.
+ * Named group permissions should be restricted by ACL_MASK.
+ */
+static void test_acl_group_with_mask(void)
+{
+	acl_t acl;
+	int err;
+
+	tst_res(TINFO, "Testing ACL_GROUP with mask");
+	reset_test_path();
+
+	acl = acl_init(5);
+	if (!acl)
+		tst_brk(TBROK | TERRNO, "acl_init failed");
+
+	add_acl_entry(acl, ACL_USER_OBJ,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_empty_acl_entry(acl, ACL_GROUP_OBJ);
+	add_named_group_acl_entry(acl, user2_gid,
+				  ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_acl_entry(acl, ACL_MASK,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_empty_acl_entry(acl, ACL_OTHER);
+
+	set_acl_file(TESTDIR, ACL_TYPE_ACCESS, acl);
+	safe_acl_free(acl);
+
+	err = try_create_as(user2_uid, user2_gid, 0644);
+	if (err) {
+		errno = err;
+		tst_res(TFAIL | TERRNO,
+			"ACL_GROUP with mask rwx should allow access");
+		return;
+	}
+
+	cleanup_testfile();
+
+	acl = acl_get_file(TESTDIR, ACL_TYPE_ACCESS);
+	if (!acl)
+		tst_brk(TBROK | TERRNO, "acl_get_file failed");
+
+	clear_acl_mask_perms(acl);
+	set_acl_file(TESTDIR, ACL_TYPE_ACCESS, acl);
+	safe_acl_free(acl);
+
+	err = try_create_as(user2_uid, user2_gid, 0644);
+	if (!err) {
+		cleanup_testfile();
+		tst_res(TFAIL, "ACL_GROUP with mask --- should deny access");
+		return;
+	}
+
+	if (err != EACCES) {
+		errno = err;
+		tst_res(TFAIL | TERRNO, "Expected EACCES from named group");
+		return;
+	}
+
+	tst_res(TPASS, "ACL_GROUP with mask works correctly");
+}
+
+/*
+ * Test ACL_GROUP_OBJ permissions with mask.
+ * Group owner permissions should be restricted by ACL_MASK.
+ */
+static void test_acl_group_obj_with_mask(void)
+{
+	acl_t acl;
+	int err;
+
+	tst_res(TINFO, "Testing ACL_GROUP_OBJ with mask");
+	reset_test_path();
+
+	SAFE_CHOWN(TESTDIR, user1_uid, user2_gid);
+
+	acl = acl_init(4);
+	if (!acl)
+		tst_brk(TBROK | TERRNO, "acl_init failed");
+
+	add_acl_entry(acl, ACL_USER_OBJ,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_acl_entry(acl, ACL_GROUP_OBJ,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_acl_entry(acl, ACL_MASK,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+	add_empty_acl_entry(acl, ACL_OTHER);
+
+	set_acl_file(TESTDIR, ACL_TYPE_ACCESS, acl);
+	safe_acl_free(acl);
+
+	err = try_create_as(user2_uid, user2_gid, 0644);
+	if (err) {
+		errno = err;
+		tst_res(TFAIL | TERRNO,
+			"ACL_GROUP_OBJ with mask rwx should allow access");
+		return;
+	}
+
+	cleanup_testfile();
+
+	acl = acl_get_file(TESTDIR, ACL_TYPE_ACCESS);
+	if (!acl)
+		tst_brk(TBROK | TERRNO, "acl_get_file failed");
+
+	clear_acl_mask_perms(acl);
+	set_acl_file(TESTDIR, ACL_TYPE_ACCESS, acl);
+	safe_acl_free(acl);
+
+	err = try_create_as(user2_uid, user2_gid, 0644);
+	if (!err) {
+		cleanup_testfile();
+		SAFE_CHOWN(TESTDIR, user1_uid, user1_gid);
+		tst_res(TFAIL,
+			"ACL_GROUP_OBJ with mask --- should deny access");
+		return;
+	}
+
+	if (err != EACCES) {
+		SAFE_CHOWN(TESTDIR, user1_uid, user1_gid);
+		errno = err;
+		tst_res(TFAIL | TERRNO, "Expected EACCES from group owner");
+		return;
+	}
+
+	SAFE_CHOWN(TESTDIR, user1_uid, user1_gid);
+	tst_res(TPASS, "ACL_GROUP_OBJ with mask works correctly");
+}
+
+static void setup(void)
+{
+	init_test_users();
+	reset_test_path();
+}
+
+static void cleanup(void)
+{
+	cleanup_test_paths();
+	cleanup_test_users();
+}
+
+static void run(unsigned int n)
+{
+	switch (n) {
+	case 0:
+		test_acl_user_with_mask();
+		break;
+	case 1:
+		test_acl_group_with_mask();
+		break;
+	case 2:
+		test_acl_group_obj_with_mask();
+		break;
+	}
+}
+
+static struct tst_test test = {
+	.test = run,
+	.tcnt = 3,
+	.setup = setup,
+	.cleanup = cleanup,
+	.needs_root = 1,
+	.mount_device = 1,
+	.mntpoint = MNTPOINT,
+	.forks_child = 1,
+	.filesystems = (struct tst_fs[]) {
+		{.type = "ext2", .mnt_data = "acl"},
+		{.type = "ext3", .mnt_data = "acl"},
+		{.type = "ext4", .mnt_data = "acl"},
+		{.type = "xfs"},
+		{.type = "btrfs"},
+		{}
+	},
+	.needs_cmds = (struct tst_cmd[]) {
+		{.cmd = "useradd"},
+		{.cmd = "userdel"},
+		{}
+	}
+};
+
+#else
+TST_TEST_TCONF("libacl or ACL headers are not available");
+#endif
-- 
2.39.1


-- 
Mailing list info: https://lists.linux.it/listinfo/ltp