Created attachment 539 [details]
Patch to fix bug

I thought this was a bug in the PAM I'm coding, but after debugging, I found that it's actually a bug in sudo itself.

To reproduce:

1) Configure sudo to use any PAM that requests user input via the conversation API.
2) Invoke sudo so it calls this PAM for authentication.
3) Press Ctrl+Z at the input prompt.

Expected results: sudo should suspend and resume cleanly.

Actual results: sudo crashes with a segmentation fault.

Cause of issue + fix:

The sudo_conv_callback structure's closure field should contain a pointer to a getpass_closure structure. The code populates this with "&closure", but this is incorrect as the "closure" argument referenced is already a pointer. As a result, when a pointer is later read from that structure, it's read from the wrong location, causing a segmentation fault.

I tried replacing "cb.closure = &closure;" with "cb.closure = closure;" in plugins/sudoers/check.c, and it resolved the issue I was experiencing. I have attached a patch for this change.