Exec race condition exploitations

I recently learned a cool technique for exploiting exec race conditions. It was mentioned in a comment by Julien Tinnes about the 2009 pulseaudio vulnerability in Linux, and more recently by Tavis Ormandy (@taviso) about the GNU C library dynamic linker expanding $ORIGIN in setuid library search path vulnerability. I am sure that many people know this for ages, but still it was new to me and I thought it was worth a small post on it.