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In this talk, we are going to disclose two unconventional Use-after-free kernel bugs on Android we found last year, and introduce the new techniques we used to make these exploits 100% reliable.
The first bug is CVE-2017-0403, which we used to gain root privilege on almost all devices shipped with 3.10 or earlier Linux kernel last year. So far more than 14 million users have successfully rooted their smartphones with this exploit. With this vulnerability, an attacker only can overwrite the freed object at a fixed offset with a pointer to object itself. How to achieve kernel code execution with this bug can be very challenging.To solve the problem, we propose a new method which is using iovec to re-fill the freed object and compromising the pipe subsystem in kernel.In this way we can covert this unusual memory corruption to arbitrary kernel memory overwriting.
The second bug is CVE-2016-6787. The bug is an UAF due to race condition, may corrupt a critical kernel structure, and lead to the kernel crash when scheduler switched context back to attacker's process. So we'll introduce a way to freeze the attacker's process soon after UAF happened ,stop kernel from crashing, and make the exploit reliable.
In summary, this presentation gives out the new techniques of exploiting use-after-free bugs we just found in Android kernel. The ideas of exploitation are fresh, detail of bugs is also never discussed before.