fuzz: Add fuzzing infrastructure and QCOW fuzzer

Add the basic infrastructure for fuzzing along with a qcow fuzzer ported
from crosvm and adapted to our code.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

docs/fuzzing.md

@@ -0,0 +1,35 @@
+# Fuzzing in Cloud Hypervisor
+
+Cloud Hypervisor uses [cargo-fuzz](https://github.com/rust-fuzz/cargo-fuzz) for fuzzing individual components.
+
+The fuzzers are are in the `fuzz/fuzz_targets` directory
+
+## Preparation
+
+Switch to nightly: 
+
+````
+rustup override set nightly
+````
+
+Install `cargo fuzz`: 
+
+```
+cargo install cargo-fuzz
+```
+
+## Running the fuzzers
+
+e.g. To run the `qcow` fuzzer using all available CPUs:
+
+```
+cargo fuzz run qcow -j `nproc`
+```
+
+## Adding a new fuzzer
+
+```
+cargo fuzz add <new_fuzzer>
+```
+
+Inspiration for fuzzers can be found in [crosvm](https://chromium.googlesource.com/chromiumos/platform/crosvm/+/refs/heads/master/fuzz/)

fuzz/.gitignore

@@ -0,0 +1,4 @@
+
+target
+corpus
+artifacts

fuzz/Cargo.toml

@@ -0,0 +1,28 @@
+
+[package]
+name = "cloud-hypervisor-fuzz"
+version = "0.0.0"
+authors = ["Automatically generated"]
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libc = "0.2.72"
+libfuzzer-sys = "0.3"
+qcow = { path = "../qcow" }
+
+[dependencies.cloud-hypervisor]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "qcow"
+path = "fuzz_targets/qcow.rs"
+test = false
+doc = false

fuzz/fuzz_targets/qcow.rs

@@ -0,0 +1,51 @@
+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE-BSD-3-Clause file.
+
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+use libc;
+use qcow::{QcowFile, RawFile};
+use std::ffi;
+use std::fs::File;
+use std::io::{self, Cursor, Read, Seek, SeekFrom, Write};
+use std::mem::size_of;
+use std::os::unix::io::{FromRawFd, RawFd};
+
+// Take the first 64 bits of data as an address and the next 64 bits as data to
+// store there. The rest of the data is used as a qcow image.
+fuzz_target!(|bytes| {
+    if bytes.len() < 16 {
+        // Need an address and data, each are 8 bytes.
+        return;
+    }
+    let mut disk_image = Cursor::new(bytes);
+    let addr = read_u64(&mut disk_image);
+    let value = read_u64(&mut disk_image);
+    let shm = memfd_create(&ffi::CString::new("fuzz").unwrap(), 0).unwrap();
+    let mut disk_file: File = unsafe { File::from_raw_fd(shm) };
+    disk_file.write_all(&bytes[16..]).unwrap();
+    disk_file.seek(SeekFrom::Start(0)).unwrap();
+    if let Ok(mut qcow) = QcowFile::from(RawFile::new(disk_file, false)) {
+        if qcow.seek(SeekFrom::Start(addr)).is_ok() {
+            let _ = qcow.write_all(&value.to_le_bytes());
+        }
+    }
+});
+
+fn read_u64<T: Read>(readable: &mut T) -> u64 {
+    let mut buf = [0u8; size_of::<u64>()];
+    readable.read_exact(&mut buf[..]).unwrap();
+    u64::from_le_bytes(buf)
+}
+
+fn memfd_create(name: &ffi::CStr, flags: u32) -> Result<RawFd, io::Error> {
+    let res = unsafe { libc::syscall(libc::SYS_memfd_create, name.as_ptr(), flags) };
+
+    if res < 0 {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(res as RawFd)
+    }
+}