fix: Prevent TokenDecoder overflow causing substr exceptions in text summarization

src/decoder.cpp

@@ -8,6 +8,43 @@ float sigmoid(float x) {
     return 1.0 / (1.0 + std::exp(-x));
 }
 
+static bool adjustSpanToTextBounds(const Span& span, size_t textLength) {
+    // Check for negative indices (overflow to large positive values)
+    if (span.startIdx < 0 || span.endIdx < 0) {
+        return false;
+    }
+
+    // Check that indices don't exceed text length
+    if (static_cast<size_t>(span.startIdx) >= textLength ||
+        static_cast<size_t>(span.endIdx) > textLength) {
+        return false;
+    }
+
+    // Check that startIdx <= endIdx
+    if (span.startIdx > span.endIdx) {
+        return false;
+    }
+
+    return true;
+}
+
+static std::string safeCopySpanText(const Span& span, const std::string& text) {
+    // First validate span bounds
+    if (!adjustSpanToTextBounds(span, text.length())) {
+        return "";
+    }
+
+    // Double-check bounds before substr call
+    size_t startPos = static_cast<size_t>(span.startIdx);
+    size_t endPos = static_cast<size_t>(span.endIdx);
+
+    if (startPos >= text.length() || endPos > text.length() || startPos > endPos) {
+        return "";
+    }
+
+    return text.substr(startPos, endPos - startPos);
+}
+
 bool Decoder::isNested(const Span& s1, const Span& s2) {
     return (s1.startIdx <= s2.startIdx && s2.endIdx <= s1.endIdx) || (s2.startIdx <= s1.startIdx && s1.endIdx <= s2.endIdx);
 }
@@ -109,11 +146,16 @@ std::vector<std::vector<Span>> SpanDecoder::decode(
             Span span;
             span.startIdx = tokens[batch_id][startToken].start;
             span.endIdx = tokens[batch_id][endToken].end;
-            span.text = texts[batch_id].substr(span.startIdx, span.endIdx - span.startIdx);
             span.classLabel = entities[entity];
             span.prob = prob;
 
-            spans[batch_id].push_back(span);
+            // Safely extract span text with bounds checking
+            span.text = safeCopySpanText(span, texts[batch_id]);
+
+            // Skip spans with invalid indices that couldn't extract text
+            if (!span.text.empty()) {
+                spans[batch_id].push_back(span);
+            }
         }
     }
 
@@ -169,13 +211,18 @@ std::vector<std::vector<Span>> TokenDecoder::decode(
             Span span;
             span.startIdx = tokens[batch_id][startToken].start;
             span.endIdx = tokens[batch_id][endToken].end;
-            span.text = texts[batch_id].substr(span.startIdx, span.endIdx - span.startIdx);
             span.classLabel = entities[entity];
             span.prob = score_sum / n;
 
-            spans[batch_id].push_back(span);
+            // Safely extract span text with bounds checking
+            span.text = safeCopySpanText(span, texts[batch_id]);
+
+            // Skip spans with invalid indices that couldn't extract text
+            if (!span.text.empty()) {
+                spans[batch_id].push_back(span);
+            }
         }
     }
 
     return batchGreedySearch(spans, flatNer, multiLabel);
-}
+}