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--- rfc:literal_string [2023/03/28 09:46] – Text tweaks craigfrancis
+++ rfc:literal_string [2023/04/20 12:18] (current) – Notes on integer/string-concat in Python/Go | Note XHP for templating | Note use of eval | Note future scope for LiteralInteger craigfrancis
@@ Line 143: / Line 143: @@
 }
 </code>
+[[https://github.com/craigfrancis/php-is-literal-rfc/blob/main/others/python/integers.py|Python]] and [[https://github.com/craigfrancis/php-is-literal-rfc/blob/main/others/go/integers.go|Go]] support string concatenation as well.
 (On a technical note, we did test an implementation that didn't support concatenation, primarily to see if this would help reduce the performance impact even further. However, the PHP engine can sometimes still concatenate values automatically at compile-time (so concatenation appears to work in some contexts), and it didn't make much (if any) difference in regards to performance, because //concat_function()// in "zend_operators.c" uses //zend_string_extend()// (which needs to remove the //LiteralString// flag) and "zend_vm_def.h" does the same; by supporting a quick concat with an empty string (x2), which would need its flag removed as well).
@@ Line 222: / Line 224: @@
 $sql .= ' ORDER BY ' . ($fields[$sort] ?? 'u.full_name'); // A LiteralString
 </code>
+This approach stops the attacker specifying a private field (e.g. //telephone_number//, where they can determine every users telephone number by updating their own account, and seeing how that affects the order).
 There may be some exceptions, see the next section.
@@ Line 301: / Line 305: @@
 Due to this limitation, we did consider an approach to trust all integers, where Scott Arciszewski suggested the name //is_noble()//. While this is not as philosophically pure, we continued to explore this possibility because we could not find any way an Injection Vulnerability could be introduced with integers in SQL, HTML, CLI; and other contexts as well (e.g. preg, mail additional_params, XPath query, and even eval). We could not find any character encoding issues either (The closest we could find was EBCDIC, an old IBM character encoding, which encodes the 0-9 characters differently; which anyone using it would need to re-encode either way, and [[https://www.php.net/manual/en/migration80.other-changes.php#migration80.other-changes.ebcdic|EBCDIC is not supported by PHP]]). And we could not find any issue with a 64bit PHP server sending a large number to a 32bit database, because the number is being encoded as characters in a string (so that's also fine). However, the feedback received was that while safe from Injection Vulnerabilities, it becomes a more complex concept, one that might cause programmers to assume it is also safe from programmer/logic errors. Ultimately the preference was the simpler approach, that did not allow any integers (which is reinforced with the name LiteralString).
+[[https://github.com/craigfrancis/php-is-literal-rfc/blob/main/others/python/integers.py|Python]] and [[https://github.com/craigfrancis/php-is-literal-rfc/blob/main/others/go/integers.go|Go]] do not support integers either.
 ==== FAQ: Other Values ====
@@ Line 417: / Line 423: @@
 In JavaScript, there is a form of Template Literal known as [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals#tagged_templates|Tagged Templates]].
-Available since ~2015 (Firefox 34, Chrome 41, NodeJS 4); where libraries will need to use [[https://github.com/tc39/proposal-array-is-template-object|isTemplateObject]] (NodeJS can use [[https://www.npmjs.com/package/is-template-object|is-template-object]]) to make sure the function is called correctly ([[https://github.com/craigfrancis/php-is-literal-rfc/blob/main/others/npm/index.js|example]]).
+Available since ~2015 (Firefox 34, Chrome 41, NodeJS 4); where libraries should use [[https://github.com/tc39/proposal-array-is-template-object|isTemplateObject]] (NodeJS can use [[https://www.npmjs.com/package/is-template-object|is-template-object]]) to ensure the function is called correctly ([[https://github.com/craigfrancis/php-is-literal-rfc/blob/main/others/npm/index.js|example]]).
 <code javascript>
@@ Line 438: / Line 444: @@
 Instead of calling a function directly, PHP could create a //TemplateLiteral// object, providing methods like //getStringParts()// and //getValues()//, so the object can be passed to a library to check and use.
-By using a //TemplateLiteral// object, it would be possible to concatenate with //$a = ```$a b```//. Concatenation is often used to help readability, and conditionally add SQL/HTML. Supporting concatenation in other ways would be up for debate, e.g.
+By using a //TemplateLiteral// object, it would be possible to concatenate with //$a = ```{$a} b```// (e.g. to conditionally add SQL/HTML, or help readability); but other forms of concatenation would be up for debate, e.g.
 <code php>
-$sql = ```$sql AND category = $category```;
+$sql = ```{$sql} AND category = {$category}```;
 $sql = ```deleted ``` . ($archive ? ```IS NOT NULL``` :  ```IS NULL```); // Maybe?
 if ($name) {
-  $sql .= ``` AND name = $name```; // Maybe?
+  $sql .= ``` AND name = {$name}```; // Maybe?
 }
 </code>
-Consideration would be needed on if/how Tagged Templates could protect functions like //mysqli_query()//; e.g. checking Tagged Template uses no variables? In comparison, all exiting (and future) code that defines their SQL as a LiteralString can simply be accepted (see the Future Scope section for details).
+Tagged Templates might be a nice feature to have (sometimes they can be easier to read), but assuming a //__toString()// method is provided, we must also consider mis-use; e.g. in JavaScript, basic Template Literals have made it much easier for developers to create XSS vulnerabilities, where developers often don't think about HTML encoding in this context:
-Tagged Templates might be a nice feature to have (sometimes they can be easier to read); but developers often believe their Database Abstractions or Parameterised Queries have completely solved Injection Vulnerabilities (unfortunately mistakes still happen), so it would be very unlikely to get //all// developers to replace //all// of their existing LiteralStrings with Tagged Templates (note how few libraries have done this in NodeJS).
+<code javascript>
+p.innerHTML = `Hi ${name}`; // INSECURE
+</code>
-While changing the quote character is fairly easy, it is tricky to automate, time-consuming, and risky for those without tests (a typical project would be looking at changing thousands of lines of code). Any escaping functions would still need to be removed (so no advantage there). Identifying field-name variables in SQL Tagged Templates would need to be considered, and libraries could not use this until PHP 8.X is their minimum supported version.
+Consideration would be needed on if/how Tagged Templates could protect functions like //mysqli_query()//; e.g. only accept if the Tagged Template uses no variables? or could PDO, MySQLi, ODBC, etc provide Value-Objects for Identifiers? In comparison, a LiteralString can simply be accepted - so code that already uses LiteralString's would not need any modification (see Future Scope for special cases).
+Also, considering developers often (incorrectly) believe their Database Abstractions or Parameterised Queries have completely solved Injection Vulnerabilities, it would be very unlikely to get //all// developers to replace //all// of their existing LiteralStrings with Tagged Templates (note how few libraries use this in NodeJS).
+While changing the quote character is fairly easy, it's tricky to automate, time-consuming, and risky for those without tests (a typical project can easily require thousands of lines of code to be changed). Any escaping functions would still need to be removed (so no advantage there). Variables for Identifiers (e.g. field-name) in SQL Tagged Templates would need to be considered, and developers will need to wait until PHP 8.X is their minimum supported version.
 [[https://github.com/craigfrancis/php-is-literal-rfc/blob/main/alternatives/tagged-templates.php|Example]] / [[https://github.com/craigfrancis/php-is-literal-rfc/commit/1dc5f4fb425009d03a640036a1022f88c4a0533d?diff=unified|Diff]]
+[[https://docs.hhvm.com/hack/XHP/introduction|XHP]] in Hack / HHVM is similar, where it introduces an XML-like syntax that can be used for HTML templating.
 ==== Macros ====
@@ Line 573: / Line 587: @@
 ===== Open Issues =====
-None
+Additional testing of the final implementation; including extensions like [[https://www.swoole.com/|Swoole]] or [[https://openswoole.com/|OpenSwoole]].
+Should //eval()// be unable to create a LiteralString, or is too similar to:
+<code php>
+$id = ($_GET['id'] ?? NULL);
+$file = tempnam(sys_get_temp_dir(), 'literal-string');
+file_put_contents($file, '<'.'?php return '.var_export(strval($id),true).';');
+$id = require($file);
+unlink($file);
+</code>
 ===== Future Scope =====
@@ Line 579: / Line 603: @@
 ) We might re-look at //sprintf()// being able to return a LiteralString.
-) As noted by MarkR, the biggest benefit will come when this flag can be used by PDO and similar functions (//mysqli_query//, //preg_match//, //exec//, etc).
+) We might re-look at //LiteralInteger//. While this is unlikely, as it would change the zval structure, it might be possible if there is enough demand. It would also need a discussion on what happens with other operations, e.g. integer addition.
+) As noted by MarkR, the biggest benefit will come when this flag can be used by PDO and similar functions (//mysqli_query//, //preg_match//, //exec//, etc).
 However, first we need libraries to start checking the relevant inputs are a LiteralString. The library can then do their thing, and apply the appropriate escaping, which can result in a value that no longer has the LiteralString flag set, but is perfectly safe for the native functions.

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