From 3d8779b377828a69ac97c3446156449fcccedda9 Mon Sep 17 00:00:00 2001
From: relrelb <relrelbachar@gmail.com>
Date: Sat, 26 Jun 2021 16:38:52 +0300
Subject: [PATCH] swf: Ignore length mismatch in `read_action`

Flash continues in such case, so just warn instead of failing.
---
 swf/src/avm1/read.rs | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/swf/src/avm1/read.rs b/swf/src/avm1/read.rs
index a8a817d52..2bc89b223 100644
--- a/swf/src/avm1/read.rs
+++ b/swf/src/avm1/read.rs
@@ -55,18 +55,19 @@ impl<'a> Reader<'a> {
 
         let action = self.read_op(opcode, &mut length);
 
-        let end_pos = (start.as_ptr() as usize + length) as *const u8;
         if let Err(e) = action {
             return Err(Error::avm1_parse_error_with_source(opcode, e));
         }
 
         // Verify that we parsed the correct amount of data.
+        let end_pos = (start.as_ptr() as usize + length) as *const u8;
         if self.input.as_ptr() != end_pos {
-            self.input = &start[length.min(start.len())..];
             // We incorrectly parsed this action.
             // Re-sync to the expected end of the action and throw an error.
-            return Err(Error::avm1_parse_error(opcode));
+            self.input = &start[length.min(start.len())..];
+            log::warn!("Length mismatch in AVM1 action: {}", OpCode::format(opcode));
         }
+
         action
     }
 
@@ -431,4 +432,26 @@ pub mod tests {
         let action = reader.read_action().unwrap().unwrap();
         assert_eq!(action, Action::Push(vec![Value::Null, Value::Undefined]));
     }
+
+    #[test]
+    fn read_length_mismatch() {
+        let action_bytes = [
+            OpCode::ConstantPool as u8,
+            5,
+            0,
+            1,
+            0,
+            b'a',
+            0,
+            OpCode::Add as u8,
+            OpCode::Subtract as u8,
+        ];
+        let mut reader = Reader::new(&action_bytes[..], 5);
+
+        let action = reader.read_action().unwrap().unwrap();
+        assert_eq!(action, Action::ConstantPool(vec!["a".into()]));
+
+        let action = reader.read_action().unwrap().unwrap();
+        assert_eq!(action, Action::Subtract);
+    }
 }