caio/clang-p2996
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[LLDB][PythonFile] fix dangerous borrow semantics on python2

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Summary:
It is inherently unsafe to allow a python program to manipulate borrowed
memory from a python object's destructor.     It would be nice to
flush a borrowed file when python is finished with it, but it's not safe
to do on python 2.

Python 3 does not suffer from this issue.

Reviewers: labath, mgorny

Reviewed By: labath

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D69532
This commit is contained in:
Lawrence D'Anna
2019-10-30 09:45:13 -07:00
parent fbe7f5e972
commit 3071ebf7b3
2 changed files with 15 additions and 17 deletions
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28
lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp
View File

@@ -1500,21 +1500,23 @@ Expected<PythonFile> PythonFile::FromFile(File &file, const char *mode) {
PyObject *file_obj;
#if PY_MAJOR_VERSION >= 3
file_obj = PyFile_FromFd(file.GetDescriptor(), nullptr, mode, -1, nullptr,
"ignore", nullptr, 0);
"ignore", nullptr, /*closefd=*/0);
#else
// We pass ::flush instead of ::fclose here so we borrow the FILE* --
// the lldb_private::File still owns it. NetBSD does not allow
// input files to be flushed, so we have to check for that case too.
int (*closer)(FILE *);
auto opts = file.GetOptions();
if (!opts)
return opts.takeError();
if (opts.get() & File::eOpenOptionWrite)
closer = ::fflush;
else
closer = [](FILE *) { return 0; };
// I'd like to pass ::fflush here if the file is writable, so that
// when the python side destructs the file object it will be flushed.
// However, this would be dangerous. It can cause fflush to be called
// after fclose if the python program keeps a reference to the file after
// the original lldb_private::File has been destructed.
//
// It's all well and good to ask a python program not to use a closed file
// but asking a python program to make sure objects get released in a
// particular order is not safe.
//
// The tradeoff here is that if a python 2 program wants to make sure this
// file gets flushed, they'll have to do it explicitly or wait untill the
// original lldb File itself gets flushed.
file_obj = PyFile_FromFile(file.GetStream(), py2_const_cast(""),
py2_const_cast(mode), closer);
py2_const_cast(mode), [](FILE *) { return 0; });
#endif
if (!file_obj)