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[java] escape backslashes in escapeForJavadoc to stop comment breakout #3903

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[java] escape backslashes in escapeForJavadoc to stop comment breakout #3903

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6 changes: 5 additions & 1 deletion lang/java/compiler/src/main/java/org/apache/avro/compiler/specific/SpecificCompiler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1118,7 +1118,11 @@ public static String javaEscape(String o) {
* Utility for template use. Escapes comment end with HTML entities.
*/
public static String escapeForJavadoc(String s) {
return s.replace("*/", "*&#47;").replace("<", "&lt;").replace(">", "&gt;");
// Double backslashes first so a value cannot smuggle in a Unicode escape such
// as \\u002a\\u002f: javac processes Unicode escapes before comments, so an
// unneutralized \\u002a\\u002f would decode to */ inside the generated Javadoc
// and let a schema doc break out of the comment into code.
return s.replace("\\", "\\\\").replace("*/", "*&#47;").replace("<", "&lt;").replace(">", "&gt;");
}

/**
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21 changes: 21 additions & 0 deletions lang/java/compiler/src/test/java/org/apache/avro/compiler/specific/TestSpecificCompiler.java
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Expand Up @@ -1058,6 +1058,27 @@ void annotationCannotBreakOutViaStringLiteral() {
assertTrue(validAnnotationEmitted, "Valid annotation missing from generated output");
}

@Test
void docCannotBreakOutViaUnicodeEscape() {
// javac decodes Unicode escapes before it strips comments, so a schema doc
// carrying a backslash-u escape for the comment terminator decodes to that
// terminator inside the generated Javadoc and ends the comment early, turning
// the rest of the doc into code. The escaper must neutralize such escapes.
String jsonSchema = "{\n" + " \"type\": \"record\",\n" + " \"name\": \"DocInjected\",\n" + " \"fields\": [\n"
+ " {\"name\": \"value\", \"type\": \"string\", \"doc\": "
+ "\"\\\\u002a\\\\u002f public static int PWNED = 1; \\\\u002f\\\\u002a\"}\n" + " ]\n" + "}";
Collection<SpecificCompiler.OutputFile> outputs = new SpecificCompiler(SchemaParser.parseSingle(jsonSchema))
.compile();
// A Unicode escape is only decoded by javac when the leading backslash is
// preceded by an even number of backslashes. An eligible escape for a comment
// char in the generated source is the breakout; the doubled form is inert.
Pattern eligibleEscape = Pattern.compile("(?<!\\\\)(?:\\\\\\\\)*\\\\u002[afAF]");
for (SpecificCompiler.OutputFile outputFile : outputs) {
assertFalse(eligibleEscape.matcher(outputFile.contents).find(),
"Unicode-escape comment breakout present? " + outputFile.contents);
}
}

private int countOccurrences(Pattern pattern, String textToSearch) {
int count = 0;
for (Matcher matcher = pattern.matcher(textToSearch); matcher.find();) {
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