Add test for FP for py/file-not-closed

Author: owen-mc

python/ql/test/query-tests/Resources/FileNotAlwaysClosed/FileNotAlwaysClosed.expected

@@ -1,9 +1,10 @@
-| resources_test.py:4:10:4:25 | ControlFlowNode for open() | File may not be closed if $@ raises an exception. | resources_test.py:5:5:5:33 | ControlFlowNode for Attribute() | this operation |
-| resources_test.py:9:10:9:25 | ControlFlowNode for open() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
-| resources_test.py:108:11:108:20 | ControlFlowNode for open() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
-| resources_test.py:112:11:112:28 | ControlFlowNode for opener_func2() | File may not be closed if $@ raises an exception. | resources_test.py:113:5:113:22 | ControlFlowNode for Attribute() | this operation |
-| resources_test.py:123:11:123:24 | ControlFlowNode for opener_func2() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
-| resources_test.py:129:15:129:24 | ControlFlowNode for open() | File may not be closed if $@ raises an exception. | resources_test.py:130:9:130:26 | ControlFlowNode for Attribute() | this operation |
-| resources_test.py:248:11:248:25 | ControlFlowNode for open() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
-| resources_test.py:269:10:269:27 | ControlFlowNode for Attribute() | File may not be closed if $@ raises an exception. | resources_test.py:271:5:271:19 | ControlFlowNode for Attribute() | this operation |
-| resources_test.py:285:11:285:20 | ControlFlowNode for open() | File may not be closed if $@ raises an exception. | resources_test.py:287:5:287:31 | ControlFlowNode for Attribute() | this operation |
+| resources_test.py:6:10:6:25 | ControlFlowNode for open() | File may not be closed if $@ raises an exception. | resources_test.py:7:5:7:33 | ControlFlowNode for Attribute() | this operation |
+| resources_test.py:11:10:11:25 | ControlFlowNode for open() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
+| resources_test.py:110:11:110:20 | ControlFlowNode for open() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
+| resources_test.py:114:11:114:28 | ControlFlowNode for opener_func2() | File may not be closed if $@ raises an exception. | resources_test.py:115:5:115:22 | ControlFlowNode for Attribute() | this operation |
+| resources_test.py:125:11:125:24 | ControlFlowNode for opener_func2() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
+| resources_test.py:131:15:131:24 | ControlFlowNode for open() | File may not be closed if $@ raises an exception. | resources_test.py:132:9:132:26 | ControlFlowNode for Attribute() | this operation |
+| resources_test.py:250:11:250:25 | ControlFlowNode for open() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |
+| resources_test.py:271:10:271:27 | ControlFlowNode for Attribute() | File may not be closed if $@ raises an exception. | resources_test.py:273:5:273:19 | ControlFlowNode for Attribute() | this operation |
+| resources_test.py:287:11:287:20 | ControlFlowNode for open() | File may not be closed if $@ raises an exception. | resources_test.py:289:5:289:31 | ControlFlowNode for Attribute() | this operation |
+| resources_test.py:361:13:361:27 | ControlFlowNode for Attribute() | File is opened but is not closed. | file://:0:0:0:0 | (none) | this operation |

python/ql/test/query-tests/Resources/FileNotAlwaysClosed/resources_test.py

@@ -1,5 +1,7 @@
 #File not always closed
 
+import os
+
 def not_close1():
     f1 = open("filename") # $ Alert # not closed on exception
     f1.write("Error could occur")
@@ -332,3 +334,30 @@ def closed32(path):
         # due to a check that an operation is lexically contained within a `with` block (with `expr.getParent*()`)
         # not detecting this case.
         return list(wrap.read())
+
+
+class FdHolder33():
+    # Mirrors CPython's `_pyio.FileIO`: it opens a file descriptor with `os.open`,
+    # stores it in an instance attribute, and exposes it again via `fileno()`.
+    def __init__(self, path):
+        fd = os.open(path, os.O_RDONLY)
+        self._fd = fd
+
+    def fileno(self):
+        return self._fd
+
+    def close(self):
+        os.close(self._fd)
+
+def closed33(path):
+    # False positive mirroring CPython's `_pyio.open`.
+    # `holder.fileno()` merely returns the existing file descriptor; it does not
+    # open a new resource. With instance-attribute type tracking, the `os.open`
+    # source flows through `self._fd` and back out of `fileno()`, so the call
+    # `holder.fileno()` is wrongly treated as a fresh file-open whose result is
+    # never closed. The descriptor is in fact owned and closed by `holder.close()`.
+    holder = FdHolder33(path)
+    try:
+        n = holder.fileno() # $ SPURIOUS: Alert
+    finally:
+        holder.close()