fuzz: fuzz testing for VHDx block device is added

The fuzzer needs to take a larger input for the whole disk image to
be most useful. Since the file is small we can test by reading and
writing over the whole file.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
Signed-off-by: Fazla Mehrab <akm.fazla.mehrab@intel.com>

fuzz/fuzz_targets/vhdx.rs

@@ -0,0 +1,53 @@
+// Copyright © 2021 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use std::ffi;
+use std::fs::File;
+use std::io::{self, Read, Seek, SeekFrom, Write};
+use std::os::unix::io::{FromRawFd, RawFd};
+use vhdx::vhdx::Vhdx;
+
+// Populate the corpus directory with a test file:
+// truncate -s 16M /tmp/source
+// qemu-img convert -O vhdx /tmp/source fuzz/corpus/vhdx/test.vhdx
+// Run with:
+// cargo fuzz run vhdx -j 32 -- -max_len=16777216
+fuzz_target!(|bytes| {
+    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[..]).unwrap();
+    disk_file.seek(SeekFrom::Start(0)).unwrap();
+
+    if let Ok(mut vhdx) = Vhdx::new(disk_file) {
+        if vhdx.seek(SeekFrom::Start(0)).is_ok() {
+            let mut offset = 0;
+            while offset < bytes.len() {
+                let mut data = vec![0; 8192];
+                vhdx.read_exact(&mut data).ok();
+                offset += data.len();
+            }
+        }
+
+        if vhdx.seek(SeekFrom::Start(0)).is_ok() {
+            let mut offset = 0;
+            while offset < bytes.len() {
+                let data = vec![0; 8192];
+                vhdx.write_all(&data).ok();
+                offset += data.len();
+            }
+        }
+    }
+});
+
+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)
+    }
+}