Fix GH-10562: Memory leak and invalid state with consecutive ftp_nb_fget

When the user does not fully consume the data stream, but instead opens
a new one, a memory leak occurs. Moreover, the state is invalid: when
more commands arrive they'll be handled out-of-sync because the state of
the client does not match what the server is doing.
This leads to all sorts of weirdness, for example:
  Warning: ftp_nb_fget(): OK.

Fix it by gracefully closing the old data stream when a new data stream
is started.

Closes GH-11606.

NEWS

@@ -21,6 +21,8 @@ PHP                                                                        NEWS
 
 - FTP:
   . Fix context option check for "overwrite". (JonasQuinten)
+  . Fixed bug GH-10562 (Memory leak and invalid state with consecutive
+    ftp_nb_fget). (nielsdos)
 
 - GD:
   . Fix most of the external libgd test failures. (Michael Orlitzky)

ext/ftp/ftp.c

@@ -2063,6 +2063,15 @@ ftp_nb_get(ftpbuf_t *ftp, php_stream *outstream, const char *path, const size_t
 		return PHP_FTP_FAILED;
 	}
 
+	if (ftp->data != NULL) {
+		/* If there is a transfer in action, abort it.
+		 * If we don't, we get an invalid state and memory leaks when the new connection gets opened. */
+		data_close(ftp, ftp->data);
+		if (!ftp_getresp(ftp) || (ftp->resp != 226 && ftp->resp != 250)) {
+			goto bail;
+		}
+	}
+
 	if (!ftp_type(ftp, type)) {
 		goto bail;
 	}

ext/ftp/tests/gh10562.phpt

@@ -0,0 +1,40 @@
+--TEST--
+GH-10562 (Memory leak with consecutive ftp_nb_fget)
+--EXTENSIONS--
+ftp
+pcntl
+--FILE--
+<?php
+require 'server.inc';
+
+$ftp = ftp_connect('127.0.0.1', $port);
+if (!$ftp) die("Couldn't connect to the server");
+
+var_dump(ftp_login($ftp, 'anonymous', 'IEUser@'));
+
+$local_file = __DIR__ . DIRECTORY_SEPARATOR . "gh10562.txt";
+$fout = fopen($local_file, "w");
+
+// This requests more data, but we don't do the loop to fetch it.
+$ret = ftp_nb_fget($ftp, $fout, "fget", FTP_BINARY, 0);
+var_dump($ret == FTP_MOREDATA);
+
+// This aborts the previous request, fetches the whole "a story" file.
+$ret = ftp_nb_fget($ftp, $fout, "a story", FTP_BINARY, 0);
+while ($ret == FTP_MOREDATA) {
+    $ret = ftp_nb_continue($ftp);
+}
+
+fclose($fout);
+
+echo file_get_contents($local_file), "\n";
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . DIRECTORY_SEPARATOR . "gh10562.txt");
+?>
+--EXPECT--
+bool(true)
+bool(true)
+BINARYFooBar
+For sale: baby shoes, never worn.