Fork brute force attack mitigation

Attacks against vulnerable userspace applications with the purpose to break
ASLR or bypass canaries traditionally use some level of brute force with
the help of the fork system call. This is possible since when creating a
new process using fork its memory contents are the same as those of the
parent process (the process that called the fork system call). So, the
attacker can test the memory infinite times to find the correct memory
values or the correct memory addresses without worrying about crashing the
application.

Based on the above scenario it would be nice to have this detected and
mitigated, and this is the goal of this patch serie. Specifically the
following attacks are expected to be detected:

1.- Launching (fork()/exec()) a setuid/setgid process repeatedly until a
    desirable memory layout is got (e.g. Stack Clash).
2.- Connecting to an exec()ing network daemon (e.g. xinetd) repeatedly
    until a desirable memory layout is got (e.g. what CTFs do for simple
    network service).
3.- Launching processes without exec() (e.g. Android Zygote) and exposing
    state to attack a sibling.
4.- Connecting to a fork()ing network daemon (e.g. apache) repeatedly until
    the previously shared memory layout of all the other children is
    exposed (e.g. kind of related to HeartBleed).

In each case, a privilege boundary has been crossed:

Case 1: setuid/setgid process
Case 2: network to local
Case 3: privilege changes
Case 4: network to local

So, what will really be detected are fork/exec brute force attacks that
cross any of the commented bounds.

The implementation details and comparison against other existing
implementations can be found in the "Documentation" patch.

This v4 version has changed a lot from the v2. Basically the application
crash period is now compute on an on-going basis using an exponential
moving average (EMA), a detection of a brute force attack through the

130 more lines

Sorry. Drop this patch serie.

Thanks,
John Wood