Skip to content

Add some gc safety around _mysql__fetch_row #348

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Feb 5, 2020
Merged

Add some gc safety around _mysql__fetch_row #348

Changes from 2 commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
c540b40
Add some safety around _mysql__fetch_row
fried Mar 21, 2019
b5fd775
expand the commend about the gc module
fried Mar 25, 2019
1ec1aa7
Update _mysql.c
methane Feb 5, 2020
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 6 additions & 0 deletions MySQLdb/_mysql.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1284,9 +1284,15 @@ _mysql__fetch_row(
if (!self->use)
row = mysql_fetch_row(self->result);
else {
// see: https://docs.python.org/3/library/gc.html#gc.get_referrers
// This function can get a reference to the tuple r, and if that
// code is preempted while holding a ref to r, the _PyTuple_Resize
// will raise a SystemError because the ref count is 2.
PyObject_GC_UnTrack(*r);
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Move these code to _mysql_ResultObject_fetch_row.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

its pretty safe everywhere else we do it in the dangerous area where we allow threads.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

It is safe untrack soon after creatin, and track again after _PyTuple_Resize().

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

For example, convert_row may execute Python code.
Execute python code means it allows threads switching, Calling gc module, etc.

Py_BEGIN_ALLOW_THREADS is not the only danger API. There are many danger APIs
which can execute any Python code. e.g. Py_DECREF, PyObject_RichCompareBool,
PyList_Append, etc.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

ping?

Py_BEGIN_ALLOW_THREADS;
row = mysql_fetch_row(self->result);
Py_END_ALLOW_THREADS;
PyObject_GC_Track(*r);
}
if (!row && mysql_errno(&(((_mysql_ConnectionObject *)(self->conn))->connection))) {
_mysql_Exception((_mysql_ConnectionObject *)self->conn);
Expand Down