[LTP] [PATCH v1 3/8] fs/acl: Add ACL_OTHER permissions test

[Sachin Sant]

Add acl_other01 test to validate that ACL_OTHER permissions are
not affected by ACL_MASK.

The test verifies that:
- ACL_OTHER entry with rwx permissions allows access
- ACL_MASK set to --- does not restrict ACL_OTHER
- Users not matching owner, named users, or groups use ACL_OTHER

This confirms that ACL_MASK only affects ACL_USER, ACL_GROUP_OBJ,
and ACL_GROUP entries, but not ACL_OTHER.

Signed-off-by: Sachin Sant <sachinp@linux.ibm.com>
---
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@linux.ibm.com/T/#t

---
 runtest/fs                            |   1 +
 testcases/kernel/fs/acl/.gitignore    |   1 +
 testcases/kernel/fs/acl/acl_other01.c | 107 ++++++++++++++++++++++++++
 3 files changed, 109 insertions(+)
 create mode 100644 testcases/kernel/fs/acl/acl_other01.c

diff --git a/runtest/fs b/runtest/fs
index b1202dc03..4a528e08e 100644
--- a/runtest/fs
+++ b/runtest/fs
@@ -90,3 +90,4 @@ squashfs01 squashfs01
 
 acl_user_obj01 acl_user_obj01
 acl_mask01 acl_mask01
+acl_other01 acl_other01
diff --git a/testcases/kernel/fs/acl/.gitignore b/testcases/kernel/fs/acl/.gitignore
index bfcdee93d..c3ec0fad3 100644
--- a/testcases/kernel/fs/acl/.gitignore
+++ b/testcases/kernel/fs/acl/.gitignore
@@ -1,2 +1,3 @@
 /acl_user_obj01
 /acl_mask01
+/acl_other01
diff --git a/testcases/kernel/fs/acl/acl_other01.c b/testcases/kernel/fs/acl/acl_other01.c
new file mode 100644
index 000000000..e16c9ac66
--- /dev/null
+++ b/testcases/kernel/fs/acl/acl_other01.c
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) IBM, 2026
+ *
+ * Original shell test by Kai Zhao (ltcd3@cn.ibm.com)
+ * Converted to C by Sachin Sant <sachinp@linux.ibm.com>
+ */
+
+/*\
+ * Test ACL_OTHER permissions.
+ *
+ * Verify that ACL_OTHER permissions work correctly and are not affected
+ * by ACL_MASK. The ACL_OTHER entry controls access for users who don't
+ * match any other ACL entry (not the owner, not in any named user entry,
+ * not in the owning group, and not in any named group entry).
+ *
+ * Unlike ACL_USER, ACL_GROUP, and ACL_GROUP_OBJ entries, ACL_OTHER
+ * permissions are not restricted by the ACL_MASK.
+ *
+ * [Algorithm]
+ *
+ * 1. Set up ACL with rwx permissions for ACL_OTHER
+ * 2. Set ACL_MASK to --- (no permissions)
+ * 3. Attempt file creation as a user matching ACL_OTHER
+ * 4. Verify access is granted despite restrictive mask
+ */
+
+#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
+
+static void run(void)
+{
+	acl_t acl;
+	int err;
+
+	tst_res(TINFO, "Testing ACL_OTHER permissions");
+	reset_test_path();
+
+	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_empty_acl_entry(acl, ACL_GROUP_OBJ);
+	add_empty_acl_entry(acl, ACL_MASK);
+	add_acl_entry(acl, ACL_OTHER,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE);
+
+	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_OTHER rwx should allow access despite mask");
+		return;
+	}
+
+	cleanup_testfile();
+	tst_res(TPASS, "ACL_OTHER not affected by mask");
+}
+
+static void setup(void)
+{
+	init_test_users();
+	reset_test_path();
+}
+
+static void cleanup(void)
+{
+	cleanup_test_paths();
+	cleanup_test_users();
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.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