Fix #79149: SEGV in mb_convert_encoding with non-string encodings

We must not assume that `hash_entry` `IS_STRING`, but rather use
`encoding_str` which is guaranteed to be.

Author: cmb69

NEWS

@@ -16,6 +16,10 @@ PHP                                                                        NEWS
   . Fixed bug #79112 (IMAP extension can't find OpenSSL libraries at configure
     time). (Nikita)
 
+- MBString:
+  . Fixed bug #79149 (SEGV in mb_convert_encoding with non-string encodings).
+    (cmb)
+
 - MySQLnd:
   . Fixed bug #79084 (mysqlnd may fetch wrong column indexes with MYSQLI_BOTH).
     (cmb)

ext/mbstring/mbstring.c

@@ -3369,12 +3369,12 @@ PHP_FUNCTION(mb_convert_encoding)
 
 					if ( _from_encodings) {
 						l = strlen(_from_encodings);
-						n = strlen(Z_STRVAL_P(hash_entry));
+						n = strlen(ZSTR_VAL(encoding_str));
 						_from_encodings = erealloc(_from_encodings, l+n+2);
 						memcpy(_from_encodings + l, ",", 1);
-						memcpy(_from_encodings + l + 1, Z_STRVAL_P(hash_entry), Z_STRLEN_P(hash_entry) + 1);
+						memcpy(_from_encodings + l + 1, ZSTR_VAL(encoding_str), ZSTR_LEN(encoding_str) + 1);
 					} else {
-						_from_encodings = estrdup(Z_STRVAL_P(hash_entry));
+						_from_encodings = estrdup(ZSTR_VAL(encoding_str));
 					}
 					zend_string_release(encoding_str);
 				} ZEND_HASH_FOREACH_END();

ext/mbstring/tests/bug79149.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Bug #79149 (SEGV in mb_convert_encoding with non-string encodings)
+--SKIPIF--
+<?php
+if (!extension_loaded('mbstring')) die('skip mbstring extension not available');
+?>
+--FILE--
+<?php
+var_dump(mb_convert_encoding("", "UTF-8", [0]));
+var_dump(mb_convert_encoding('foo', 'UTF-8', array(['bar'], ['baz'])));
+?>
+--EXPECTF--
+Warning: mb_convert_encoding(): Illegal character encoding specified in %s on line %d
+string(0) ""
+
+Notice: Array to string conversion in %s on line %d
+
+Notice: Array to string conversion in %s on line %d
+
+Warning: mb_convert_encoding(): Illegal character encoding specified in %s on line %d
+string(3) "foo"