fuzz: Add block device fuzzer

Add the block device fuzzer that interprets the fuzz data input as
follows:
starting index 8 bytes
command location 8 bytes
command 16 bytes
descriptors circular buffer 16 bytes * 3

Change-Id: I25b58e149bfb9a479fab7955c0ca25c67c590bf6
Signed-off-by: Dylan Reid <dgreid@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/900202
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>

2 files changed, 125 insertions, 0 deletions

diff --git a/fuzz/Cargo.toml b/fuzz/Cargo.toml
index 3dd3d41..063b21c 100644
--- a/fuzz/Cargo.toml
+++ b/fuzz/Cargo.toml
@@ -15,6 +15,10 @@ sys_util = { path = "../sys_util" }
 members = ["."]
 
 [[bin]]
+name = "crosvm_block_fuzzer"
+path = "block_fuzzer.rs"
+
+[[bin]]
 name = "crosvm_qcow_fuzzer"
 path = "qcow_fuzzer.rs"
 
diff --git a/fuzz/block_fuzzer.rs b/fuzz/block_fuzzer.rs
new file mode 100644
index 0000000..5c3106a
--- /dev/null
+++ b/fuzz/block_fuzzer.rs
@@ -0,0 +1,121 @@
+// 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 file.
+
+#![no_main]
+extern crate devices;
+extern crate libc;
+extern crate sys_util;
+
+use sys_util::{EventFd, GuestAddress, GuestMemory, SharedMemory};
+
+use std::fs::File;
+use std::io::{Cursor, Read, Seek, SeekFrom};
+use std::mem::size_of;
+use std::os::unix::io::{AsRawFd, FromRawFd};
+use std::panic;
+use std::process;
+use std::slice;
+use std::sync::atomic::AtomicUsize;
+use std::sync::Arc;
+
+use devices::virtio::{Block, Queue, VirtioDevice};
+
+const MEM_SIZE: u64 = 256 * 1024 * 1024;
+const DESC_SIZE: u64 = 16; // Bytes in one virtio descriptor.
+const QUEUE_SIZE: u16 = 16; // Max entries in the queue.
+const CMD_SIZE: usize = 16; // Bytes in the command.
+
+// 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.
+#[export_name = "LLVMFuzzerTestOneInput"]
+pub fn test_one_input(data: *const u8, size: usize) -> i32 {
+    // We cannot unwind past ffi boundaries.
+    panic::catch_unwind(|| {
+        // Safe because the libfuzzer runtime will guarantee that `data` is at least
+        // `size` bytes long and that it will be valid for the lifetime of this
+        // function.
+        let bytes = unsafe { slice::from_raw_parts(data, size) };
+        let size_u64 = size_of::<u64>();
+        let mem = GuestMemory::new(&[(GuestAddress(0), MEM_SIZE)]).unwrap();
+
+        // The fuzz data is interpreted as:
+        // starting index 8 bytes
+        // command location 8 bytes
+        // command 16 bytes
+        // descriptors circular buffer 16 bytes * 3
+        if bytes.len() < 4 * size_u64 {
+            // Need an index to start.
+            return;
+        }
+
+        let mut data_image = Cursor::new(bytes);
+
+        let first_index = read_u64(&mut data_image);
+        if first_index > MEM_SIZE / DESC_SIZE {
+            return;
+        }
+        let first_offset = first_index * DESC_SIZE;
+        if first_offset as usize + size_u64 > bytes.len() {
+            return;
+        }
+
+        let command_addr = read_u64(&mut data_image);
+        if command_addr > MEM_SIZE - CMD_SIZE as u64 {
+            return;
+        }
+        if mem
+            .write_all_at_addr(
+                &bytes[2 * size_u64..(2 * size_u64) + CMD_SIZE],
+                GuestAddress(command_addr as u64),
+            )
+            .is_err()
+        {
+            return;
+        }
+
+        data_image.seek(SeekFrom::Start(first_offset)).unwrap();
+        let desc_table = read_u64(&mut data_image);
+
+        if mem
+            .write_all_at_addr(&bytes[32..], GuestAddress(desc_table as u64))
+            .is_err()
+        {
+            return;
+        }
+
+        let mut q = Queue::new(QUEUE_SIZE);
+        q.ready = true;
+        q.size = QUEUE_SIZE / 2;
+        q.max_size = QUEUE_SIZE;
+
+        let queue_evts: Vec<EventFd> = vec![EventFd::new().unwrap()];
+        let queue_fd = queue_evts[0].as_raw_fd();
+        let queue_evt = unsafe { EventFd::from_raw_fd(libc::dup(queue_fd)) };
+
+        let shm = SharedMemory::new(None).unwrap();
+        let disk_file: File = shm.into();
+        let mut block = Block::new(disk_file, false, None).unwrap();
+
+        block.activate(
+            mem,
+            EventFd::new().unwrap(),
+            EventFd::new().unwrap(),
+            Arc::new(AtomicUsize::new(0)),
+            vec![q],
+            queue_evts,
+        );
+
+        queue_evt.write(77).unwrap(); // Rings the doorbell, any byte will do.
+    })
+    .err()
+    .map(|_| process::abort());
+
+    0
+}
+
+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)
+}