What to know prior to open-sourcing a project from legal perspective?

Previous questions and answers are focusing on "usability" and promotion (as if we are living in some ideal world). I am wondering what could be potential negative legal consequences.

For example:

1) using a patent algorithm without consideration (e.g. now expired http://ift.tt/1ABS2vm);

2) violating an existing trademark (e.g. http://ift.tt/1EcU0Kc);

What is the procedure of open-sourcing in huge bureaucratic companies (e.g. Google, Apple, Goldman Sachs)?