solana: Add overflow checks, tests, and fuzzing

Add simple fuzz harness for TrimmedAmount::trim
Add overflow checks for issues discovered while fuzzing
Add unit tests to verify that errors are returned from overflow checks
Add new errors (in ntt-messages and in the Anchor custom errors)
Add some additional documentation for functions

Author: johnsaigle

solana/fuzz/src/Cargo.lock

@@ -0,0 +1,15 @@
+[package]
+name = "ntt-fuzz"
+version = "0.0.1"
+
+[[bin]]
+name = "ntt-fuzz"
+path = "fuzz_trimmed_amount.rs"
+
+edition = "2021"
+[dependencies]
+ntt-messages = { path = "../../modules/ntt-messages" }
+honggfuzz = "0.5"
+arbitrary = { version = "1", optional = true, features = ["derive"] }
+
+[workspace]

solana/fuzz/src/Cargo.toml

@@ -0,0 +1,31 @@
+# Fuzzing
+
+Requires honggfuzz. Fuzz tests will not run on Apple Silicon.
+
+## Install
+
+```bash
+cargo install honggfuzz
+```
+
+## Build
+
+```bash
+# in solana/fuzz/src
+cargo hfuzz build
+```
+
+## Run
+
+```bash
+cargo hfuzz run ntt-fuzz
+```
+
+As more targets are added, other targets for `run` can be found and added as `bins` defined in `Cargo.toml`.
+`name` corresponds to the binary used by `cargo hfuzz run`.
+```toml
+...
+[[bin]]
+name = "ntt-fuzz"
+...
+```

solana/fuzz/src/README.md

@@ -0,0 +1,13 @@
+use honggfuzz::fuzz;
+use ntt_messages::trimmed_amount::TrimmedAmount;
+
+// #[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
+
+fn main() {
+    loop {
+         fuzz!(|input: (u64, u8, u8)| {
+
+            let _ = TrimmedAmount::trim(input.0, input.1, input.2);
+        });
+    }
+}

solana/fuzz/src/fuzz_trimmed_amount.rs

@@ -0,0 +1,23 @@
+use std::fmt::{Display, Formatter};
+
+#[derive(Debug, PartialEq)]
+pub enum ScalingError {
+    OverflowExponent,
+    OverflowScaledAmount,
+}
+
+impl std::error::Error for ScalingError {}
+
+impl Display for ScalingError {
+    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
+        match self {
+            ScalingError::OverflowExponent => write!(
+                f,
+                "Overflow: scaling factor exponent exceeds the max value of u64"
+            ),
+            ScalingError::OverflowScaledAmount => {
+                write!(f, "Overflow: scaled amount exceeds the max value of u64")
+            }
+        }
+    }
+}

solana/modules/ntt-messages/src/errors.rs

@@ -1,4 +1,5 @@
 pub mod chain_id;
+pub mod errors;
 pub mod mode;
 pub mod ntt;
 pub mod ntt_manager;