Multiprocessors May Reduce System Dependability under File-Based Race Condition Attacks

Attacks exploiting race conditions have been considered rare and "low risk". However, the increasing popularity of multiprocessors has changed this situation: instead of waiting for the victim process to be suspended to carry out an attack, the attacker can now run on a dedicated processor and actively seek attack opportunities. This change from fortuitous encountering to active exploiting may greatly increase the success probability of race condition attacks. This point is exemplified by studying the TOCTTOU (Time-of- Check-to-Time-of-Use) race condition attacks in this paper. We first propose a probabilistic model for predicting TOCTTOU attack success rate on both uniprocessors and multiprocessors. Then we confirm the applicability of this model by carrying out TOCTTOU attacks against two widely used utility programs: vi and gedit. The success probability of attacking vi increases from low single digit percentage on a uniprocessor to almost 100% on a multiprocessor. Similarly, the success rate of attacking gedit jumps from almost zero to 83%. These case studies suggest that our model captures the sharply increased risks, and hence the decreased dependability of our systems, represented by race condition attacks such as TOCTTOU on the next generation multiprocessors.