byxtest: add test cases for the RECORD extension CVEs of the last years

Commit 2902b78535 ("Fix XRecordRegisterClients() Integer underflow")

Assisted-by: Claude:claude-claude-opus-4-6
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2187>

test/pyxtest/meson.build

@@ -56,6 +56,7 @@ if pytest.found()
     # This needs to be kept in sync with the test_foo.py files in the tree
     tests_pyxtest = [
         'test_randr.py',
+        'test_record.py',
         'test_xi.py',
         'test_xkb.py',
     ]

test/pyxtest/proto/record.py

@@ -0,0 +1,82 @@
+# SPDX-License-Identifier: MIT
+#
+# RECORD extension protocol request builders
+
+import struct
+from dataclasses import dataclass, field
+
+# RECORD minor opcodes
+RecordQueryVersion = 0
+RecordCreateContext = 1
+RecordRegisterClients = 2
+
+RECORD_MAJOR = 1
+RECORD_MINOR = 13
+
+
+@dataclass
+class QueryVersionRequest:
+    """RecordQueryVersion request."""
+
+    opcode: int
+    major: int = RECORD_MAJOR
+    minor: int = RECORD_MINOR
+
+    def to_bytes(self, byte_order: str = "<") -> bytes:
+        return struct.pack(
+            f"{byte_order}BBHHH",
+            self.opcode,
+            RecordQueryVersion,
+            2,
+            self.major,
+            self.minor,
+        )
+
+
+@dataclass
+class CreateContextRequest:
+    """RecordCreateContext request.
+
+    Header is 20 bytes, followed by nClients CARD32 client IDs,
+    then nRanges xRecordRange structs (32 bytes each).
+    """
+
+    opcode: int
+    context_id: int
+    element_header: int = 0
+    client_ids: list[int] = field(default_factory=list)
+    ranges_data: bytes = b""
+    n_clients_override: int | None = None
+    n_ranges_override: int | None = None
+
+    def to_bytes(self, byte_order: str = "<") -> bytes:
+        n_clients = (
+            self.n_clients_override
+            if self.n_clients_override is not None
+            else len(self.client_ids)
+        )
+        n_ranges = (
+            self.n_ranges_override
+            if self.n_ranges_override is not None
+            else len(self.ranges_data) // 32
+        )
+
+        client_data = b""
+        for cid in self.client_ids:
+            client_data += struct.pack(f"{byte_order}I", cid)
+
+        total_bytes = 20 + len(client_data) + len(self.ranges_data)
+        pad_len = (4 - total_bytes % 4) % 4
+        total_bytes += pad_len
+
+        header = struct.pack(
+            f"{byte_order}BBH I B xxx I I",
+            self.opcode,
+            RecordCreateContext,
+            total_bytes // 4,
+            self.context_id,
+            self.element_header,
+            n_clients,
+            n_ranges,
+        )
+        return header + client_data + self.ranges_data + b"\x00" * pad_len

test/pyxtest/test_record.py

@@ -0,0 +1,67 @@
+# SPDX-License-Identifier: MIT
+#
+# Security tests for RECORD extension vulnerabilities.
+
+import time
+
+import pytest
+
+from proto import record
+from xclient import Extension
+
+
+@pytest.fixture
+def record_xclient_swapped(xclient_swapped):
+    """Provide a byte-swapped xclient with RECORD initialized."""
+    ext = xclient_swapped.query_extension(Extension.RECORD)
+    if not ext:
+        pytest.skip("RECORD extension not available")
+
+    req = record.QueryVersionRequest(opcode=ext.opcode)
+    xclient_swapped.send_request(req.to_bytes(">"))
+    xclient_swapped.recv_response(timeout=5.0)
+
+    return xclient_swapped, ext.opcode
+
+
+class TestRecordCreateContext:
+    """Tests for RECORD CreateContext/RegisterClients vulnerabilities."""
+
+    @pytest.mark.swapped_client
+    @pytest.mark.asan
+    def test_swap_create_register_integer_underflow(
+        self, xserver, record_xclient_swapped
+    ):
+        """
+        CVE-2020-14362 / ZDI-CAN-11574: SwapCreateRegister() used
+        stuff->length (attacker-controlled 16-bit wire field) instead
+        of client->req_len for bounds checking nClients.
+
+        With big requests or a carefully crafted length field, the
+        subtraction ``stuff->length - header_size`` can underflow,
+        allowing nClients to pass the check and causing OOB reads
+        during client ID swapping.
+
+        Fixed in commit 2902b78535ec ("Fix XRecordRegisterClients() Integer
+        underflow").
+        """
+        conn, opcode = record_xclient_swapped
+
+        ctx_id = conn.alloc_id()
+
+        # Send CreateContext claiming many clients but with
+        # minimal actual data.
+        req = record.CreateContextRequest(
+            opcode=opcode,
+            context_id=ctx_id,
+            client_ids=[0],  # One client ID
+            ranges_data=b"\x00" * 32,  # One range (32 bytes)
+            n_clients_override=100,  # Claim 100 clients
+            n_ranges_override=1,
+        )
+        conn.send_request(req.to_bytes(">"))
+        time.sleep(0.5)
+
+        assert xserver.is_alive, (
+            "Server crashed - integer underflow in SwapCreateRegister (CVE-2020-14362)"
+        )