test: Experiment with cargo fuzz (#1764)

* test: Experiment with `cargo fuzz`

Far from being ready.

* Fix

* Fixes

* Fixes

* Make clippy happy

* Another clippy fix

* Fuzz `Frame::decode`

* Rework

* Fix clippy

* Try and disable on Windows

* Retry

* Retry

* Try again

* Review suggestions

* Clippy

* Update Cargo.toml

Co-authored-by: Martin Thomson <mt@lowentropy.net>
Signed-off-by: Lars Eggert <lars@eggert.org>

* Update neqo-transport/src/packet/mod.rs

Co-authored-by: Martin Thomson <mt@lowentropy.net>
Signed-off-by: Lars Eggert <lars@eggert.org>

* Rename directory to `fuzz`

* `lazy_static` -> `OnceLock`

* * Add ability to save items to fuzzing corpus via
  `build-fuzzing-corpus` feature.

* Disable RNG and encryption during fuzzing and corpus generation

* Misc. other fixes.

* Clippy

* `DefaultHasher` is not in `std::hash` yet in Rust 1.74

* Add two more fuzzers

* Tweaks

* Don't check coverage for fuzzing code

* Update neqo-common/src/fuzz.rs

Co-authored-by: Martin Thomson <mt@lowentropy.net>
Signed-off-by: Lars Eggert <lars@eggert.org>

* Update neqo-transport/src/connection/mod.rs

Co-authored-by: Martin Thomson <mt@lowentropy.net>
Signed-off-by: Lars Eggert <lars@eggert.org>

* Update neqo-transport/src/connection/mod.rs

Co-authored-by: Martin Thomson <mt@lowentropy.net>
Signed-off-by: Lars Eggert <lars@eggert.org>

* Update neqo-crypto/src/p11.rs

Co-authored-by: Martin Thomson <mt@lowentropy.net>
Signed-off-by: Lars Eggert <lars@eggert.org>

* Fixups

* More fixups

* Remove `fuzz/src/lib.rs` now that #1830 is merged

* Fix merge

* Create corpus directory if it does not exist

* Use a predictable sequence of bytes for `disable-random` instead of just zeros.

* Update neqo-common/src/lib.rs

Co-authored-by: Martin Thomson <mt@lowentropy.net>
Signed-off-by: Lars Eggert <lars@eggert.org>

* Use thread-local instead of atomic

* Only write generated packets, and only ones without test frames

* Build a corpus for `client_initial` and `server_initial` fuzz targets

* Cleanup

---------

Signed-off-by: Lars Eggert <lars@eggert.org>
Co-authored-by: Max Inden <mail@max-inden.de>
Co-authored-by: Martin Thomson <mt@lowentropy.net>

.codecov.yml

@@ -1,5 +1,6 @@
-# neqo has no test coverage for its example client and server
+# neqo has no test coverage for its example client and server, and for the fuzzing code.
 ignore:
+  - "fuzz"
   - "neqo-bin"
   - "test-fixture"
 

Cargo.toml

@@ -1,5 +1,6 @@
 [workspace]
 members = [
+  "fuzz",
   "neqo-bin",
   "neqo-common",
   "neqo-crypto",

fuzz/.gitignore

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

fuzz/Cargo.toml

@@ -0,0 +1,52 @@
+[package]
+name = "fuzz"
+authors.workspace = true
+homepage.workspace = true
+repository.workspace = true
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+neqo-common = { path = "../neqo-common" }
+neqo-crypto = { path = "../neqo-crypto" }
+neqo-transport = { path = "../neqo-transport" }
+test-fixture = { path = "../test-fixture" }
+
+[target.'cfg(not(windows))'.dependencies]
+libfuzzer-sys = { version = "0.4" }
+
+[lints]
+workspace = true
+
+[[bin]]
+name = "packet"
+path = "fuzz_targets/packet.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "frame"
+path = "fuzz_targets/frame.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "client_initial"
+path = "fuzz_targets/client_initial.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "server_initial"
+path = "fuzz_targets/server_initial.rs"
+test = false
+doc = false
+bench = false

fuzz/fuzz_targets/client_initial.rs

@@ -0,0 +1,73 @@
+#![cfg_attr(all(fuzzing, not(windows)), no_main)]
+
+#[cfg(all(fuzzing, not(windows)))]
+use libfuzzer_sys::fuzz_target;
+
+#[cfg(all(fuzzing, not(windows)))]
+fuzz_target!(|data: &[u8]| {
+    use neqo_common::{Datagram, Encoder, Role};
+    use neqo_transport::Version;
+    use test_fixture::{
+        default_client, default_server,
+        header_protection::{
+            apply_header_protection, decode_initial_header, initial_aead_and_hp,
+            remove_header_protection,
+        },
+        now,
+    };
+
+    let mut client = default_client();
+    let ci = client.process(None, now()).dgram().expect("a datagram");
+    let Some((header, d_cid, s_cid, payload)) = decode_initial_header(&ci, Role::Client) else {
+        return;
+    };
+    let (aead, hp) = initial_aead_and_hp(d_cid, Role::Client);
+    let (_, pn) = remove_header_protection(&hp, header, payload);
+
+    let mut payload_enc = Encoder::with_capacity(1200);
+    payload_enc.encode(data); // Add fuzzed data.
+
+    // Make a new header with a 1 byte packet number length.
+    let mut header_enc = Encoder::new();
+    header_enc
+        .encode_byte(0xc0) // Initial with 1 byte packet number.
+        .encode_uint(4, Version::default().wire_version())
+        .encode_vec(1, d_cid)
+        .encode_vec(1, s_cid)
+        .encode_vvec(&[])
+        .encode_varint(u64::try_from(payload_enc.len() + aead.expansion() + 1).unwrap())
+        .encode_byte(u8::try_from(pn).unwrap());
+
+    let mut ciphertext = header_enc.as_ref().to_vec();
+    ciphertext.resize(header_enc.len() + payload_enc.len() + aead.expansion(), 0);
+    let v = aead
+        .encrypt(
+            pn,
+            header_enc.as_ref(),
+            payload_enc.as_ref(),
+            &mut ciphertext[header_enc.len()..],
+        )
+        .unwrap();
+    assert_eq!(header_enc.len() + v.len(), ciphertext.len());
+    // Pad with zero to get up to 1200.
+    ciphertext.resize(1200, 0);
+
+    apply_header_protection(
+        &hp,
+        &mut ciphertext,
+        (header_enc.len() - 1)..header_enc.len(),
+    );
+    let fuzzed_ci = Datagram::new(
+        ci.source(),
+        ci.destination(),
+        ci.tos(),
+        ci.ttl(),
+        ciphertext,
+    );
+
+    let mut server = default_server();
+    let _response = server.process(Some(&fuzzed_ci), now());
+});
+
+#[cfg(any(not(fuzzing), windows))]
+fn main() {}

fuzz/fuzz_targets/frame.rs

@@ -0,0 +1,17 @@
+#![cfg_attr(all(fuzzing, not(windows)), no_main)]
+
+#[cfg(all(fuzzing, not(windows)))]
+use libfuzzer_sys::fuzz_target;
+
+#[cfg(all(fuzzing, not(windows)))]
+fuzz_target!(|data: &[u8]| {
+    use neqo_common::Decoder;
+    use neqo_transport::frame::Frame;
+
+    // Run the fuzzer
+    let mut decoder = Decoder::new(data);
+    let _ = Frame::decode(&mut decoder);
+});
+
+#[cfg(any(not(fuzzing), windows))]
+fn main() {}

fuzz/fuzz_targets/packet.rs

@@ -0,0 +1,21 @@
+#![cfg_attr(all(fuzzing, not(windows)), no_main)]
+
+#[cfg(all(fuzzing, not(windows)))]
+use libfuzzer_sys::fuzz_target;
+
+#[cfg(all(fuzzing, not(windows)))]
+fuzz_target!(|data: &[u8]| {
+    use std::sync::OnceLock;
+
+    use neqo_transport::{packet::PublicPacket, RandomConnectionIdGenerator};
+
+    static DECODER: OnceLock<RandomConnectionIdGenerator> = OnceLock::new();
+    let decoder = DECODER.get_or_init(|| RandomConnectionIdGenerator::new(20));
+    neqo_crypto::init().unwrap();
+
+    // Run the fuzzer
+    let _ = PublicPacket::decode(data, decoder);
+});
+
+#[cfg(any(not(fuzzing), windows))]
+fn main() {}

fuzz/fuzz_targets/server_initial.rs

@@ -0,0 +1,77 @@
+#![cfg_attr(all(fuzzing, not(windows)), no_main)]
+
+#[cfg(all(fuzzing, not(windows)))]
+use libfuzzer_sys::fuzz_target;
+
+#[cfg(all(fuzzing, not(windows)))]
+fuzz_target!(|data: &[u8]| {
+    use neqo_common::{Datagram, Encoder, Role};
+    use neqo_transport::Version;
+    use test_fixture::{
+        default_client, default_server,
+        header_protection::{
+            apply_header_protection, decode_initial_header, initial_aead_and_hp,
+            remove_header_protection,
+        },
+        now,
+    };
+
+    let mut client = default_client();
+    let ci = client.process(None, now()).dgram().expect("a datagram");
+    let mut server = default_server();
+    let si = server
+        .process(Some(&ci), now())
+        .dgram()
+        .expect("a datagram");
+
+    let Some((header, d_cid, s_cid, payload)) = decode_initial_header(&si, Role::Server) else {
+        return;
+    };
+    let (aead, hp) = initial_aead_and_hp(d_cid, Role::Server);
+    let (_, pn) = remove_header_protection(&hp, header, payload);
+
+    let mut payload_enc = Encoder::with_capacity(1200);
+    payload_enc.encode(data); // Add fuzzed data.
+
+    // Make a new header with a 1 byte packet number length.
+    let mut header_enc = Encoder::new();
+    header_enc
+        .encode_byte(0xc0) // Initial with 1 byte packet number.
+        .encode_uint(4, Version::default().wire_version())
+        .encode_vec(1, d_cid)
+        .encode_vec(1, s_cid)
+        .encode_vvec(&[])
+        .encode_varint(u64::try_from(payload_enc.len() + aead.expansion() + 1).unwrap())
+        .encode_byte(u8::try_from(pn).unwrap());
+
+    let mut ciphertext = header_enc.as_ref().to_vec();
+    ciphertext.resize(header_enc.len() + payload_enc.len() + aead.expansion(), 0);
+    let v = aead
+        .encrypt(
+            pn,
+            header_enc.as_ref(),
+            payload_enc.as_ref(),
+            &mut ciphertext[header_enc.len()..],
+        )
+        .unwrap();
+    assert_eq!(header_enc.len() + v.len(), ciphertext.len());
+    // Pad with zero to get up to 1200.
+    ciphertext.resize(1200, 0);
+
+    apply_header_protection(
+        &hp,
+        &mut ciphertext,
+        (header_enc.len() - 1)..header_enc.len(),
+    );
+    let fuzzed_si = Datagram::new(
+        si.source(),
+        si.destination(),
+        si.tos(),
+        si.ttl(),
+        ciphertext,
+    );
+    let _response = client.process(Some(&fuzzed_si), now());
+});
+
+#[cfg(any(not(fuzzing), windows))]
+fn main() {}

neqo-common/Cargo.toml

@@ -16,6 +16,7 @@ workspace = true
 # Sync with https://searchfox.org/mozilla-central/source/Cargo.lock 2024-02-08
 enum-map = { version = "2.7", default-features = false }
 env_logger = { version = "0.10", default-features = false }
+hex = { version = "0.4", default-features = false, features = ["alloc"], optional = true }
 log = { workspace = true }
 qlog = { workspace = true }
 time = { version = "0.3", default-features = false, features = ["formatting"] }
@@ -26,6 +27,7 @@ test-fixture = { path = "../test-fixture" }
 
 [features]
 ci = []
+build-fuzzing-corpus = ["hex"]
 
 [target."cfg(windows)".dependencies.winapi]
 version = "0.3"

neqo-common/src/fuzz.rs

@@ -0,0 +1,43 @@
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::{
+    collections::hash_map::DefaultHasher,
+    fs::File,
+    hash::{Hash, Hasher},
+    io::Write,
+    path::Path,
+};
+
+/// Write a data item `data` for the fuzzing target `target` to the fuzzing corpus. The caller needs
+/// to make sure that `target` is the correct fuzzing target name for the data written.
+///
+/// # Panics
+///
+/// Panics if the corpus directory does not exist or if the corpus item cannot be written.
+pub fn write_item_to_fuzzing_corpus(target: &str, data: &[u8]) {
+    // This bakes in the assumption that we're executing in the root of the neqo workspace.
+    // Unfortunately, `cargo fuzz` doesn't provide a way to learn the location of the corpus
+    // directory.
+    let corpus = Path::new("../fuzz/corpus").join(target);
+    if !corpus.exists() {
+        std::fs::create_dir_all(&corpus).expect("failed to create corpus directory");
+    }
+
+    // Hash the data to get a unique name for the corpus item.
+    let mut hasher = DefaultHasher::new();
+    data.hash(&mut hasher);
+    let item_name = hex::encode(hasher.finish().to_be_bytes());
+    let item_path = corpus.join(item_name);
+    if item_path.exists() {
+        // Don't overwrite existing corpus items.
+        return;
+    }
+
+    // Write the data to the corpus item.
+    let mut file = File::create(item_path).expect("failed to create corpus item");
+    Write::write_all(&mut file, data).expect("failed to write to corpus item");
+}

neqo-common/src/lib.rs

@@ -9,6 +9,8 @@
 mod codec;
 mod datagram;
 pub mod event;
+#[cfg(feature = "build-fuzzing-corpus")]
+mod fuzz;
 pub mod header;
 pub mod hrtime;
 mod incrdecoder;
@@ -21,6 +23,8 @@ use std::fmt::Write;
 
 use enum_map::Enum;
 
+#[cfg(feature = "build-fuzzing-corpus")]
+pub use self::fuzz::write_item_to_fuzzing_corpus;
 pub use self::{
     codec::{Decoder, Encoder},
     datagram::Datagram,

neqo-crypto/Cargo.toml

@@ -30,8 +30,9 @@ toml = { version = "0.5", default-features = false }
 test-fixture = { path = "../test-fixture" }
 
 [features]
-gecko = ["mozbuild"]
 disable-encryption = []
+disable-random = []
+gecko = ["mozbuild"]
 
 [lib]
 # See https://github.com/bheisler/criterion.rs/blob/master/book/src/faq.md#cargo-bench-gives-unrecognized-option-errors-for-valid-command-line-options