From 92cc75b3ae9ea4b344f4a43dba29d0d0e0c6baf0 Mon Sep 17 00:00:00 2001
From: "mergify[bot]" <37929162+mergify[bot]@users.noreply.github.com>
Date: Thu, 27 Jan 2022 13:02:42 +0000
Subject: [PATCH] test_ed25519 fails if we randomly select index 1 (#22779)

(cherry picked from commit c1b543c74d18e1342f57756a38e6c956ee2711c0)

# Conflicts:
#       sdk/src/ed25519_instruction.rs

Co-authored-by: Sean Young <sean@mess.org>
---
 programs/ed25519/src/lib.rs    | 9 ++++++++-
 sdk/src/ed25519_instruction.rs | 1 +
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/programs/ed25519/src/lib.rs b/programs/ed25519/src/lib.rs
index b0496f02cf..7f4dc8b730 100644
--- a/programs/ed25519/src/lib.rs
+++ b/programs/ed25519/src/lib.rs
@@ -44,7 +44,14 @@ pub mod test {
 
         assert!(tx.verify_precompiles(&feature_set).is_ok());
 
-        let index = thread_rng().gen_range(0, instruction.data.len());
+        let index = loop {
+            let index = thread_rng().gen_range(0, instruction.data.len());
+            // byte 1 is not used, so this would not cause the verify to fail
+            if index != 1 {
+                break index;
+            }
+        };
+
         instruction.data[index] = instruction.data[index].wrapping_add(12);
         let tx = Transaction::new_signed_with_payer(
             &[instruction],
diff --git a/sdk/src/ed25519_instruction.rs b/sdk/src/ed25519_instruction.rs
index 911b31e80b..ae7a3c9395 100644
--- a/sdk/src/ed25519_instruction.rs
+++ b/sdk/src/ed25519_instruction.rs
@@ -108,6 +108,7 @@ pub fn verify_signatures(data: &[u8], instruction_datas: &[&[u8]]) -> Result<(),
     let expected_data_size = num_signatures
         .saturating_mul(SIGNATURE_OFFSETS_SERIALIZED_SIZE)
         .saturating_add(SIGNATURE_OFFSETS_START);
+    // We do not check or use the byte at data[1]
     if data.len() < expected_data_size {
         return Err(Ed25519Error::InvalidInstructionDataSize);
     }