Skip to content

bpo-32818: Fix a subprocess crash in Windows compatiblity mode #5948

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

Closed
segevfiner wants to merge 2 commits into from
Closed

bpo-32818: Fix a subprocess crash in Windows compatiblity mode #5948

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
ba73c81
bpo-32818: Fix a subprocess crash in Windows compatiblity mode
segevfiner Mar 1, 2018
b50e4de
Merge remote-tracking branch 'upstream/main' into bpo-32818-create-pr…
segevfiner Feb 21, 2022
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
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Windows/2018-03-01-14-00-51.bpo-32818.C_908x.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a subprocess crash in Windows compatibility mode when
``STARTUPINFO.lpAttributeList`` is empty. Patch By Segev Finer.
3 changes: 2 additions & 1 deletion Modules/_winapi.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1140,7 +1140,8 @@ _winapi_CreateProcess_impl(PyObject *module,
NULL,
NULL,
inherit_handles,
creation_flags | EXTENDED_STARTUPINFO_PRESENT |
creation_flags |
(si.lpAttributeList ? EXTENDED_STARTUPINFO_PRESENT : 0) |

@eryksun eryksun Mar 1, 2018 •
edited
Loading

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

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

It may be more resilient to also always allocate an attribute list, even if it's empty. That avoids any potential Windows bugs where a bad assumption is made based on the struct size and ignoring the creation flags. This could be done with the following changes in getattributelist:

value = PyObject_GetAttrString(obj, name);

if (!value) {
    PyErr_Clear();
    Py_INCREF(Py_None);
    value = Py_None;
} else if (value != Py_None && !PyMapping_Check(value)) {
    ret = -1;
    PyErr_Format(PyExc_TypeError, "%s must be a mapping or None", name);
    goto cleanup;
}

if (value != Py_None) {
    attribute_list->handle_list = gethandlelist(value, "handle_list",
        &handle_list_size);
    if (attribute_list->handle_list == NULL && PyErr_Occurred()) {
        ret = -1;
        goto cleanup;
    }
}

@segevfiner segevfiner Mar 1, 2018

Copy link
Copy Markdown
Contributor Author

Choose a reason for hiding this comment

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

Since this will always allocate the attribute list, it makes the change to the flags passed to CreateProcess redundant. I was contemplating a fix like this too. But I'm not sure which is the best or more robust fix for this.

@eryksun eryksun Mar 1, 2018

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

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

The simplest and most efficient solution is to omit the creation flag, as you implemented it. In Windows 10, the extended startup info creation flag gates further checks. If it's present in the creation flags, and the startup info is the right size, and the attribute list pointer isn't NULL, then CreateProcess calls BasepConvertWin32AttributeList to convert the attribute list to NT form. If the struct is the wrong size, it's handled as an invalid parameter.

That said, I'm more comfortable if the startup info is valid on its own. The docs don't explicitly say it's ok for lpAttributeList to be NULL, but I assumed it was. It's common for an optional parameter or field to be set to NULL when unused. If we omit the creation flag that indicates an extended startup info is present when we're actually using an extended startup info (as indicated by size, but then the flag is redundant), to me that seems like a nonsense hack. In that case I'd rather allocate an empty attribute list.

@ghost ghost Mar 10, 2018

Copy link
Copy Markdown

Choose a reason for hiding this comment

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

I don't know how to fix.

I would suggest that add a comment like this, since this patch may be removed in several years later.

/* fix a bug of Windows Compatiblity Mode, bpo-32818 */

CREATE_UNICODE_ENVIRONMENT,
wenvironment,
current_directory,
Expand Down