Fix infinite recursion on deprecated attribute evaluation

Fixes GH-17711

Zend/tests/gh17711.phpt

@@ -0,0 +1,18 @@
+--TEST--
+GH-17711: Infinite recursion through deprecated class constants self-referencing through deprecation message
+--FILE--
+<?php
+
+const TEST = 'Message';
+
+class C {
+    #[\Deprecated(self::C)]
+    const C = TEST;
+}
+
+var_dump(C::C);
+
+?>
+--EXPECTF--
+Deprecated: Constant C::C is deprecated, Message in %s on line %d
+string(7) "Message"

Zend/zend_constants.c

@@ -353,8 +353,10 @@ ZEND_API zval *zend_get_class_constant_ex(zend_string *class_name, zend_string *
 			}
 
 			if (UNEXPECTED(ZEND_CLASS_CONST_FLAGS(c) & ZEND_ACC_DEPRECATED)) {
-				if ((flags & ZEND_FETCH_CLASS_SILENT) == 0) {
+				if ((flags & ZEND_FETCH_CLASS_SILENT) == 0 && !CONST_IS_RECURSIVE(c)) {
+					CONST_PROTECT_RECURSION(c);
 					zend_deprecated_class_constant(c, constant_name);
+					CONST_UNPROTECT_RECURSION(c);
 					if (EG(exception)) {
 						goto failure;
 					}

Zend/zend_constants.h

@@ -27,6 +27,21 @@
 #define CONST_NO_FILE_CACHE		(1<<1)				/* Can't be saved in file cache */
 #define CONST_DEPRECATED		(1<<2)				/* Deprecated */
 #define CONST_OWNED				(1<<3)				/* constant should be destroyed together with class */
+#define CONST_RECURSIVE			(1<<4)				/* Recursion protection for constant evaluation */
+
+#define CONST_IS_RECURSIVE(c) (Z_CONSTANT_FLAGS((c)->value) & CONST_RECURSIVE)
+#define CONST_PROTECT_RECURSION(c) \
+	do { \
+		if (Z_TYPE((c)->value) == IS_CONSTANT_AST) { \
+			Z_CONSTANT_FLAGS((c)->value) |= CONST_RECURSIVE; \
+		} \
+	} while (0)
+#define CONST_UNPROTECT_RECURSION(zval) \
+	do { \
+		if (Z_TYPE((c)->value) == IS_CONSTANT_AST) { \
+			Z_CONSTANT_FLAGS((c)->value) &= ~CONST_RECURSIVE; \
+		} \
+	} while (0)
 
 #define	PHP_USER_CONSTANT   0x7fffff /* a constant defined in user space */
 

Zend/zend_vm_def.h

@@ -6094,8 +6094,10 @@ ZEND_VM_HANDLER(181, ZEND_FETCH_CLASS_CONSTANT, VAR|CONST|UNUSED|CLASS_FETCH, CO
 			}
 
 			bool is_constant_deprecated = ZEND_CLASS_CONST_FLAGS(c) & ZEND_ACC_DEPRECATED;
-			if (UNEXPECTED(is_constant_deprecated)) {
+			if (UNEXPECTED(is_constant_deprecated) && !CONST_IS_RECURSIVE(c)) {
+				CONST_PROTECT_RECURSION(c);
 				zend_deprecated_class_constant(c, constant_name);
+				CONST_UNPROTECT_RECURSION(c);
 
 				if (EG(exception)) {
 					ZVAL_UNDEF(EX_VAR(opline->result.var));