fix mac UAF from async buffer read in update_with_buffer_stride - #401

Hey, Thanks for the PR!

Can you describe more what this code fixes?

The synchronous [view draw] does fix the UAF, since replaceRegion:withBytes: copies the buffer before mfb_update_with_buffer returns.

Two suggestions:

1. Clear the pointer after the draw, so any stray draw can never read freed memory (drawInMTKView already guards on a NULL buffer):

[view draw];
win->draw_parameters->buffer = NULL;

2. view.paused = YES with the default enableSetNeedsDisplay = NO means the view only draws on the explicit [view draw]. During a live resize drag AppKit's tracking loop blocks the app's update loop, so the window shows a stale stretched frame until the drag ends. With the pointer cleared as above, it's safe to also set view.enableSetNeedsDisplay = YES so resize/expose repaints still work.

Makes sense, thank you for the suggestions! I am new to this. I ran into this bug doing my first project in rust.

When trying out the change there, I see the window being drawn while drag moved, but not while being drag resized. I am unsure if I have it misconfigured or if there is something else I am missing.

hum... I don't have access to a mac right now, but I can try it out to tomorrow.

Sorry, I haven't managed to get around to check this yet. Will try as soon as I can

I had a look and what I think we need to do is to remove this line

view.enableSetNeedsDisplay = YES;

The issue is that to fix the resize issue with this enabled requires quite bit of more changes when this is enabled, which I think need it's own PR.

Gotcha, just removed that line

Cool. Does this solve the current resize issue?

Sorry for the late response! I'm still seeing the resize issue on my project. Maybe that should be a separate issue still?

Sounds good!