ext/ftp: fix out-of-bounds read in ftp_get() ASCII CRLF translation

In ASCII mode ftp_get() peeks at the byte after each '\r' to fold CRLF
into LF. When that '\r' is the last byte of a full FTP_BUFSIZE read, the
lookahead reads one byte past the buffer; a server placing '\r' at
offset 4095 of a 4096-byte read hits it (ASAN: heap-buffer-overflow
read of size 1). Bound the lookahead to the received data, as
ftp_readline() does. ftp_nb_continue_read() carries the trailing '\r'
across reads and isn't affected.

Closes GH-22328

Author: iliaal

ext/ftp/ftp.c

@@ -946,7 +946,7 @@ ftp_get(ftpbuf_t *ftp, php_stream *outstream, const char *path, const size_t pat
 #else
 			while (e > ptr && (s = memchr(ptr, '\r', (e - ptr)))) {
 				php_stream_write(outstream, ptr, (s - ptr));
-				if (*(s + 1) == '\n') {
+				if (s + 1 < e && *(s + 1) == '\n') {
 					s++;
 					php_stream_putc(outstream, '\n');
 				}

ext/ftp/tests/ftp_get_ascii_crlf_boundary.phpt

@@ -0,0 +1,25 @@
+--TEST--
+ftp_get() ASCII mode: CRLF straddling the FTP_BUFSIZE read boundary
+--EXTENSIONS--
+ftp
+pcntl
+--FILE--
+<?php
+require 'server.inc';
+
+$ftp = ftp_connect('127.0.0.1', $port);
+ftp_login($ftp, 'user', 'pass');
+$ftp or die("Couldn't connect to the server");
+
+$local = __DIR__ . "/crlf_boundary_out.txt";
+
+var_dump(ftp_get($ftp, $local, 'crlf_boundary', FTP_ASCII));
+var_dump(file_get_contents($local) === str_repeat("A", 4095) . "\n" . str_repeat("B", 10));
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/crlf_boundary_out.txt");
+?>
+--EXPECT--
+bool(true)
+bool(true)

ext/ftp/tests/server.inc

@@ -391,6 +391,13 @@ if ($pid) {
                     // Just a side channel for getting the received file size.
                     fputs($s, "425 Can't open data connection (".$GLOBALS['rest_pos'].").\r\n");
                     break;
+                case "crlf_boundary":
+                    // A CRLF whose CR lands on the final byte of the first
+                    // FTP_BUFSIZE (4096) read, so the LF arrives in the next read.
+                    fputs($s, "150 File status okay; about to open data connection.\r\n");
+                    fputs($fs, str_repeat("A", 4095) . "\r\n" . str_repeat("B", 10));
+                    fputs($s, "226 Closing data Connection.\r\n");
+                    break;
 
                 default:
                     fputs($s, "550 {$matches[1]}: No such file or directory \r\n");