fuzz: disable tests unless 'cfg(fuzzing)' is passed; update README for reproducing failures

fuzz/README.md

@@ -65,4 +65,29 @@ If it is working, you will see a rapid stream of data for many seconds
 (you can hit Ctrl+C to stop it early). If not, you should quickly see
 an error.
 
+# Reproducing Failures
+
+If a fuzztest fails, it will exit with a summary which looks something like
+
+```
+...
+ fuzzTarget      : hfuzz_target/x86_64-unknown-linux-gnu/release/hashes_sha256 
+CRASH:
+DESCRIPTION: 
+ORIG_FNAME: 00000000000000000000000000000000.00000000.honggfuzz.cov
+FUZZ_FNAME: hfuzz_workspace/hashes_sha256/SIGABRT.PC.7ffff7c8abc7.STACK.18826d9b64.CODE.-6.ADDR.0.INSTR.mov____%eax,%ebp.fuzz
+...
+=====================================================================
+fff400610004
+```
+
+The final line is a hex-encoded version of the input that caused the crash. You
+can test this directly by editing the `duplicate_crash` test to copy/paste the
+hex output into the call to `extend_vec_from_hex`. Then run the test with
+
+    RUSTFLAGS=--cfg=fuzzing cargo test
+
+It is important to add the `cfg=fuzzing` flag, which tells rustc to compile the
+library as though it were running a fuzztest. In particular, this will disable
+or weaken all the cryptography.
 

fuzz/fuzz_targets/bitcoin/deser_net_msg.rs

@@ -13,7 +13,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_address.rs

@@ -19,7 +19,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_amount.rs

@@ -36,7 +36,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_block.rs

@@ -13,7 +13,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_prefilled_transaction.rs

@@ -22,7 +22,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_psbt.rs

@@ -22,7 +22,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_script.rs

@@ -52,7 +52,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_transaction.rs

@@ -34,7 +34,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/deserialize_witness.rs

@@ -18,7 +18,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/outpoint_string.rs

@@ -49,7 +49,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/bitcoin/script_bytes_to_asm_fmt.rs

@@ -23,3 +23,30 @@ fn main() {
         });
     }
 }
+
+#[cfg(all(test, fuzzing))]
+mod tests {
+    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
+        let mut b = 0;
+        for (idx, c) in hex.as_bytes().iter().enumerate() {
+            b <<= 4;
+            match *c {
+                b'A'..=b'F' => b |= c - b'A' + 10,
+                b'a'..=b'f' => b |= c - b'a' + 10,
+                b'0'..=b'9' => b |= c - b'0',
+                _ => panic!("Bad hex"),
+            }
+            if (idx & 1) == 1 {
+                out.push(b);
+                b = 0;
+            }
+        }
+    }
+
+    #[test]
+    fn duplicate_crash() {
+        let mut a = Vec::new();
+        extend_vec_from_hex("00000", &mut a);
+        super::do_test(&a);
+    }
+}

fuzz/fuzz_targets/hashes/cbor.rs

@@ -28,7 +28,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/hashes/json.rs

@@ -28,7 +28,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/hashes/ripemd160.rs

@@ -20,7 +20,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/hashes/sha1.rs

@@ -20,7 +20,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/hashes/sha256.rs

@@ -20,7 +20,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;
@@ -42,7 +42,7 @@ mod tests {
     #[test]
     fn duplicate_crash() {
         let mut a = Vec::new();
-        extend_vec_from_hex("00000", &mut a);
+        extend_vec_from_hex("fff400610004", &mut a);
         super::do_test(&a);
     }
 }

fuzz/fuzz_targets/hashes/sha512.rs

@@ -20,7 +20,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;

fuzz/fuzz_targets/hashes/sha512_256.rs

@@ -20,7 +20,7 @@ fn main() {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, fuzzing))]
 mod tests {
     fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
         let mut b = 0;