ext/standard: Fix symlink trying to resolve dangling links

Author: zaaarf

ext/standard/link.c

@@ -131,11 +131,21 @@ PHP_FUNCTION(symlink)
 	char dirname[MAXPATHLEN];
 	size_t len;
 
+	zend_stat_t v_lstat = {0};
+	zend_stat_t v_stat = {0};
+
 	ZEND_PARSE_PARAMETERS_START(2, 2)
 		Z_PARAM_PATH(topath, topath_len)
 		Z_PARAM_PATH(frompath, frompath_len)
 	ZEND_PARSE_PARAMETERS_END();
 
+	// dangling link should be treated as existing file
+	ret = VCWD_LSTAT(frompath, &v_lstat);
+	if (!ret && S_ISLNK(v_lstat.st_mode) && VCWD_STAT(frompath, &v_stat)) {
+		php_error_docref(NULL, E_WARNING, "File exists in %s", frompath);
+		RETURN_FALSE;
+	}
+
 	if (!expand_filepath(frompath, source_p)) {
 		php_error_docref(NULL, E_WARNING, "No such file or directory");
 		RETURN_FALSE;

ext/standard/tests/gh21992t.phpt

@@ -0,0 +1,76 @@
+--TEST--
+GH-21992: symlink() must not resolve the final dangling link component
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY === 'Windows') {
+    die('not for Windows');
+}
+?>
+--FILE--
+<?php
+$dir = __DIR__ . '/gh21992';
+$targetDir = $dir . '/target_dir';
+
+// dangling link to nonexisting $ghost
+$deadLink = $dir . '/dead_link.txt';
+$ghost = $targetDir . '/ghost.txt';
+$newTarget = $dir . '/nothing';
+
+// real link to $realFile
+$realLink = $dir . '/real_link.txt';
+$realFile = $targetDir . '/real.txt';
+$realTarget = $dir . '/something';
+
+mkdir($dir);
+mkdir($targetDir);
+touch($realFile); // ensure $realFile exists
+
+// verify the real file works fine
+var_dump(symlink($realFile, $realLink));
+var_dump(readlink($realLink));
+var_dump(symlink($realTarget, $realLink));
+var_dump(is_link($realLink));
+var_dump(readlink($realLink));
+var_dump(is_link($realFile));
+
+// verify the ghost file works as intended
+var_dump(symlink($ghost, $deadLink));
+var_dump(readlink($deadLink));
+var_dump(symlink($newTarget, $deadLink));
+var_dump(is_link($deadLink));
+var_dump(readlink($deadLink));
+var_dump(is_link($ghost));
+?>
+--CLEAN--
+<?php
+$dir = __DIR__ . '/gh21992';
+$targetDir = $dir . '/target_dir';
+$deadLink = $dir . '/dead_link.txt';
+$ghost = $targetDir . '/ghost.txt';
+$realLink = $dir . '/real_link.txt';
+$realFile = $targetDir . '/real.txt';
+
+@unlink($ghost);
+@unlink($deadLink);
+@unlink($realLink);
+@unlink($realFile);
+@rmdir($targetDir);
+@rmdir($dir);
+?>
+--EXPECTF--
+bool(true)
+string(%d) "%s/gh21992/target_dir/real.txt"
+
+Warning: symlink(): File exists in %s on line %d
+bool(false)
+bool(true)
+string(%d) "%s/gh21992/target_dir/real.txt"
+bool(false)
+bool(true)
+string(%d) "%s/gh21992/target_dir/ghost.txt"
+
+Warning: symlink(): File exists in %s on line %d
+bool(false)
+bool(true)
+string(%d) "%s/gh21992/target_dir/ghost.txt"
+bool(false)