[LTP] [PATCH v11 3/8] fs/acl: Add ACL_OTHER permission test

[Sachin Sant]

Add test to verify ACL_OTHER permissions work correctly and are not
restricted by ACL_MASK.

The test sets up an ACL with:
- ACL_OTHER with rwx permissions
- ACL_MASK with no permissions (---)
- Verifies that a user matching ACL_OTHER can still create files

This validates that ACL_OTHER permissions are applied directly without
mask restriction, as specified in POSIX ACL semantics.

Suggested-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Sachin Sant <sachinp@linux.ibm.com>
---
No changes in V7 to V11

V6 changes:
- Added HAVE_SYS_XATTR_H guard
- Removed redundant error checking, relying on library functions
- Updated algorithm documentation with correct format
- v5 link https://lore.kernel.org/ltp/20260608092200.92827-1-sachinp@linux.ibm.com/T/#t

V5 changes:
- Switch to kernel only test validation to remove dependency on libacl
  and useradd/del commands.
- v3 link https://lore.kernel.org/ltp/20260604065417.25924-1-sachinp@linux.ibm.com/T/#t

V4 changes:
- No change
V3 changes:
- Updated copyright header as per LTP format.
- v1 link https://lore.kernel.org/ltp/20260602121958.27494-1-sachinp@linux.ibm.com/T/#t

V2 changes:
- No change

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 | 104 ++++++++++++++++++++++++++
 3 files changed, 106 insertions(+)
 create mode 100644 testcases/kernel/fs/acl/acl_other01.c

diff --git a/runtest/fs b/runtest/fs
index 69ecb8647..f25487a33 100644
--- a/runtest/fs
+++ b/runtest/fs
@@ -91,3 +91,4 @@ squashfs01 squashfs01
 # Run the acl tests
 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..41349223e
--- /dev/null
+++ b/testcases/kernel/fs/acl/acl_other01.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 IBM
+ *
+ * Original shell test by Kai Zhao (ltcd3@cn.ibm.com)
+ * Converted to C by Sachin Sant <sachinp@linux.ibm.com>
+ */
+
+/*\
+ * Test ACL_OTHER permissions using direct xattr manipulation.
+ *
+ * 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.
+ *
+ * This test uses arbitrary UIDs without creating actual users, testing
+ * only the kernel ACL implementation.
+ *
+ * [Algorithm]
+ *
+ * - Set up ACL with rwx permissions for ACL_OTHER
+ * - Set ACL_MASK to --- (no permissions)
+ * - Attempt file creation as a user matching ACL_OTHER
+ * - Verify access is granted despite restrictive mask
+ */
+
+#include "acl_lib.h"
+
+#ifdef HAVE_SYS_XATTR_H
+
+#define TEST_UID 1000
+#define TEST_GID 1000
+#define OTHER_UID 2000
+#define OTHER_GID 2000
+
+static void run(void)
+{
+	struct acl *acl;
+
+	tst_res(TINFO, "Testing ACL_OTHER permissions");
+	reset_test_path();
+
+	SAFE_CHOWN(TESTDIR, TEST_UID, TEST_GID);
+
+	acl = acl_init();
+
+	acl_add_entry(acl, ACL_USER_OBJ,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE, 0);
+	acl_add_entry(acl, ACL_GROUP_OBJ, 0, 0);
+	acl_add_entry(acl, ACL_MASK, 0, 0);
+	acl_add_entry(acl, ACL_OTHER,
+		      ACL_READ | ACL_WRITE | ACL_EXECUTE, 0);
+
+	if (acl_set_file(TESTDIR, ACL_TYPE_ACCESS, acl) < 0) {
+		if (errno == EOPNOTSUPP) {
+			acl_free(acl);
+			tst_brk(TCONF | TERRNO, "ACL not supported");
+		}
+		acl_free(acl);
+		tst_brk(TBROK | TERRNO, "ACL setup failed");
+	}
+
+	acl_free(acl);
+
+	try_create_as(OTHER_UID, OTHER_GID, 0644, 0);
+
+	cleanup_testfile();
+}
+
+static void setup(void)
+{
+	reset_test_path();
+}
+
+static void cleanup(void)
+{
+	cleanup_test_paths();
+}
+
+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"},
+		{}
+	}
+};
+
+#else
+	TST_TEST_TCONF("sys/xattr.h is not available");
+#endif
-- 
2.39.1