Respond to 1.1 A2 (also cited as 2 1)

`read_vec` was unbounded. It now accepts an optional bound. In some places, we
are able to define and provide a bound (Bulletproofs(+)' `L` and `R` vectors).
In others, we cannot (the amount of inputs within a transaction, which is not
subject to any rule in the current consensus other than the total transaction
size limit). Usage of `None` in those locations preserves the existing
behavior.

networks/monero/generators/src/lib.rs

@@ -51,8 +51,6 @@ pub fn H_pow_2() -> &'static [EdwardsPoint; 64] {
 pub const MAX_COMMITMENTS: usize = 16;
 /// The amount of bits a value within a commitment may use.
 pub const COMMITMENT_BITS: usize = 64;
-/// The logarithm (over 2) of the amount of bits a value within a commitment may use.
-pub const LOG_COMMITMENT_BITS: usize = 6; // 2 ** 6 == N
 
 /// Container struct for Bulletproofs(+) generators.
 #[allow(non_snake_case)]

networks/monero/io/src/lib.rs

@@ -214,6 +214,20 @@ pub fn read_array<R: Read, T: Debug, F: Fn(&mut R) -> io::Result<T>, const N: us
 }
 
 /// Read a length-prefixed variable-length list of elements.
-pub fn read_vec<R: Read, T, F: Fn(&mut R) -> io::Result<T>>(f: F, r: &mut R) -> io::Result<Vec<T>> {
-  read_raw_vec(f, read_varint(r)?, r)
+///
+/// An optional bound on the length of the result may be provided. If `None`, the returned `Vec`
+/// will be of the length read off the reader, if successfully read. If `Some(_)`, an error will be
+/// raised if the length read off the read is greater than the bound.
+pub fn read_vec<R: Read, T, F: Fn(&mut R) -> io::Result<T>>(
+  f: F,
+  length_bound: Option<usize>,
+  r: &mut R,
+) -> io::Result<Vec<T>> {
+  let declared_length: usize = read_varint(r)?;
+  if let Some(length_bound) = length_bound {
+    if declared_length > length_bound {
+      Err(io::Error::other("vector exceeds bound on length"))?;
+    }
+  }
+  read_raw_vec(f, declared_length, r)
 }

networks/monero/primitives/src/lib.rs

@@ -213,7 +213,7 @@ impl Decoys {
   pub fn write(&self, w: &mut impl io::Write) -> io::Result<()> {
     write_vec(write_varint, &self.offsets, w)?;
     w.write_all(&[self.signer_index])?;
-    write_vec(
+    write_raw_vec(
       |pair, w| {
         write_point(&pair[0], w)?;
         write_point(&pair[1], w)
@@ -239,10 +239,12 @@ impl Decoys {
   /// This is not a Monero protocol defined struct, and this is accordingly not a Monero protocol
   /// defined serialization.
   pub fn read(r: &mut impl io::Read) -> io::Result<Decoys> {
+    let offsets = read_vec(read_varint, None, r)?;
+    let len = offsets.len();
     Decoys::new(
-      read_vec(read_varint, r)?,
+      offsets,
       read_byte(r)?,
-      read_vec(|r| Ok([read_point(r)?, read_point(r)?]), r)?,
+      read_raw_vec(|r| Ok([read_point(r)?, read_point(r)?]), len, r)?,
     )
     .ok_or_else(|| io::Error::other("invalid Decoys"))
   }

networks/monero/ringct/bulletproofs/src/core.rs

@@ -6,7 +6,7 @@ use curve25519_dalek::{
   edwards::EdwardsPoint,
 };
 
-pub(crate) use monero_generators::{MAX_COMMITMENTS, COMMITMENT_BITS, LOG_COMMITMENT_BITS};
+pub(crate) use monero_generators::{MAX_COMMITMENTS, COMMITMENT_BITS};
 
 pub(crate) fn multiexp(pairs: &[(Scalar, EdwardsPoint)]) -> EdwardsPoint {
   let mut buf_scalars = Vec::with_capacity(pairs.len());

networks/monero/ringct/bulletproofs/src/lib.rs

@@ -17,13 +17,13 @@ use curve25519_dalek::edwards::EdwardsPoint;
 
 use monero_io::*;
 pub use monero_generators::MAX_COMMITMENTS;
+use monero_generators::COMMITMENT_BITS;
 use monero_primitives::Commitment;
 
 pub(crate) mod scalar_vector;
 pub(crate) mod point_vector;
 
 pub(crate) mod core;
-use crate::core::LOG_COMMITMENT_BITS;
 
 pub(crate) mod batch_verifier;
 use batch_verifier::{BulletproofsBatchVerifier, BulletproofsPlusBatchVerifier};
@@ -44,6 +44,11 @@ use crate::plus::{
 #[cfg(test)]
 mod tests;
 
+// The logarithm (over 2) of the amount of bits a value within a commitment may use.
+const LOG_COMMITMENT_BITS: usize = COMMITMENT_BITS.ilog2() as usize;
+// The maximum length of L/R `Vec`s.
+const MAX_LR: usize = (MAX_COMMITMENTS.ilog2() as usize) + LOG_COMMITMENT_BITS;
+
 /// An error from proving/verifying Bulletproofs(+).
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 #[cfg_attr(feature = "std", derive(thiserror::Error))]
@@ -265,8 +270,8 @@ impl Bulletproof {
       tau_x: read_scalar(r)?,
       mu: read_scalar(r)?,
       ip: IpProof {
-        L: read_vec(read_point, r)?,
-        R: read_vec(read_point, r)?,
+        L: read_vec(read_point, Some(MAX_LR), r)?,
+        R: read_vec(read_point, Some(MAX_LR), r)?,
         a: read_scalar(r)?,
         b: read_scalar(r)?,
       },
@@ -284,8 +289,8 @@ impl Bulletproof {
         r_answer: read_scalar(r)?,
         s_answer: read_scalar(r)?,
         delta_answer: read_scalar(r)?,
-        L: read_vec(read_point, r)?.into_iter().collect(),
-        R: read_vec(read_point, r)?.into_iter().collect(),
+        L: read_vec(read_point, Some(MAX_LR), r)?.into_iter().collect(),
+        R: read_vec(read_point, Some(MAX_LR), r)?.into_iter().collect(),
       },
     }))
   }

networks/monero/src/transaction.rs

@@ -71,7 +71,7 @@ impl Input {
         let amount = if amount == 0 { None } else { Some(amount) };
         Input::ToKey {
           amount,
-          key_offsets: read_vec(read_varint, r)?,
+          key_offsets: read_vec(read_varint, None, r)?,
           key_image: read_torsion_free_point(r)?,
         }
       }
@@ -241,7 +241,7 @@ impl TransactionPrefix {
   pub fn read<R: Read>(r: &mut R, version: u64) -> io::Result<TransactionPrefix> {
     let additional_timelock = Timelock::read(r)?;
 
-    let inputs = read_vec(|r| Input::read(r), r)?;
+    let inputs = read_vec(|r| Input::read(r), None, r)?;
     if inputs.is_empty() {
       Err(io::Error::other("transaction had no inputs"))?;
     }
@@ -250,10 +250,10 @@ impl TransactionPrefix {
     let mut prefix = TransactionPrefix {
       additional_timelock,
       inputs,
-      outputs: read_vec(|r| Output::read((!is_miner_tx) && (version == 2), r), r)?,
+      outputs: read_vec(|r| Output::read((!is_miner_tx) && (version == 2), r), None, r)?,
       extra: vec![],
     };
-    prefix.extra = read_vec(read_byte, r)?;
+    prefix.extra = read_vec(read_byte, None, r)?;
     Ok(prefix)
   }
 

networks/monero/wallet/src/extra.rs

@@ -181,16 +181,10 @@ impl ExtraField {
         size
       }),
       1 => ExtraField::PublicKey(read_point(r)?),
-      2 => ExtraField::Nonce({
-        let nonce = read_vec(read_byte, r)?;
-        if nonce.len() > MAX_TX_EXTRA_NONCE_SIZE {
-          Err(io::Error::other("too long nonce"))?;
-        }
-        nonce
-      }),
+      2 => ExtraField::Nonce(read_vec(read_byte, Some(MAX_TX_EXTRA_NONCE_SIZE), r)?),
       3 => ExtraField::MergeMining(read_varint(r)?, read_bytes(r)?),
-      4 => ExtraField::PublicKeys(read_vec(read_point, r)?),
-      0xDE => ExtraField::MysteriousMinergate(read_vec(read_byte, r)?),
+      4 => ExtraField::PublicKeys(read_vec(read_point, None, r)?),
+      0xDE => ExtraField::MysteriousMinergate(read_vec(read_byte, None, r)?),
       _ => Err(io::Error::other("unknown extra field"))?,
     })
   }

networks/monero/wallet/src/send/mod.rs

@@ -456,7 +456,7 @@ impl SignableTransaction {
   /// defined serialization.
   pub fn read<R: io::Read>(r: &mut R) -> io::Result<SignableTransaction> {
     fn read_address<R: io::Read>(r: &mut R) -> io::Result<MoneroAddress> {
-      String::from_utf8(read_vec(read_byte, r)?)
+      String::from_utf8(read_vec(read_byte, None, r)?)
         .ok()
         .and_then(|str| MoneroAddress::from_str_with_unchecked_network(&str).ok())
         .ok_or_else(|| io::Error::other("invalid address"))
@@ -484,9 +484,9 @@ impl SignableTransaction {
       rct_type: RctType::try_from(read_byte(r)?)
         .map_err(|()| io::Error::other("unsupported/invalid RctType"))?,
       outgoing_view_key: Zeroizing::new(read_bytes(r)?),
-      inputs: read_vec(OutputWithDecoys::read, r)?,
-      payments: read_vec(read_payment, r)?,
-      data: read_vec(|r| read_vec(read_byte, r), r)?,
+      inputs: read_vec(OutputWithDecoys::read, None, r)?,
+      payments: read_vec(read_payment, None, r)?,
+      data: read_vec(|r| read_vec(read_byte, None, r), None, r)?,
       fee_rate: FeeRate::read(r)?,
     };
     match res.validate() {