From patchwork Fri Aug 26 15:27:46 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 12956227 X-Patchwork-Delegate: kuba@kernel.org Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3224ECAAD4 for ; Fri, 26 Aug 2022 15:29:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244258AbiHZP3h (ORCPT ); Fri, 26 Aug 2022 11:29:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344484AbiHZP3R (ORCPT ); Fri, 26 Aug 2022 11:29:17 -0400 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 72164DEB72 for ; Fri, 26 Aug 2022 08:27:49 -0700 (PDT) Received: from fsav115.sakura.ne.jp (fsav115.sakura.ne.jp [27.133.134.242]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 27QFRlRp086469; Sat, 27 Aug 2022 00:27:47 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav115.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav115.sakura.ne.jp); Sat, 27 Aug 2022 00:27:47 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav115.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 27QFRkNj086466 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Sat, 27 Aug 2022 00:27:47 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <345de429-a88b-7097-d177-adecf9fed342@I-love.SAKURA.ne.jp> Date: Sat, 27 Aug 2022 00:27:46 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: [PATCH] 9p/trans_fd: always use O_NONBLOCK read/write Content-Language: en-US To: Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , Christian Schoenebeck References: <00000000000039af4d05915a9f56@google.com> <000000000000c1d3ca0593128b24@google.com> Cc: syzbot , v9fs-developer@lists.sourceforge.net, syzkaller-bugs@googlegroups.com, netdev@vger.kernel.org From: Tetsuo Handa In-Reply-To: <000000000000c1d3ca0593128b24@google.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org syzbot is reporting hung task at p9_fd_close() [1], for p9_mux_poll_stop() from p9_conn_destroy() from p9_fd_close() is failing to interrupt already started kernel_read() from p9_fd_read() from p9_read_work() and/or kernel_write() from p9_fd_write() from p9_write_work() requests. Since p9_socket_open() sets O_NONBLOCK flag, p9_mux_poll_stop() does not need to interrupt kernel_read()/kernel_write(). However, since p9_fd_open() does not set O_NONBLOCK flag, but pipe blocks unless signal is pending, p9_mux_poll_stop() needs to interrupt kernel_read()/kernel_write() when the file descriptor refers to a pipe. In other words, pipe file descriptor needs to be handled as if socket file descriptor. We somehow need to interrupt kernel_read()/kernel_write() on pipes. A minimal change, which this patch is doing, is to set O_NONBLOCK flag from p9_fd_open(), for O_NONBLOCK flag does not affect reading/writing of regular files. But this approach changes O_NONBLOCK flag on userspace- supplied file descriptors (which might break userspace programs), and O_NONBLOCK flag could be changed by userspace. It would be possible to set O_NONBLOCK flag every time p9_fd_read()/p9_fd_write() is invoked, but still remains small race window for clearing O_NONBLOCK flag. If we don't want to manipulate O_NONBLOCK flag, we might be able to surround kernel_read()/kernel_write() with set_thread_flag(TIF_SIGPENDING) and recalc_sigpending(). Since p9_read_work()/p9_write_work() works are processed by kernel threads which process global system_wq workqueue, signals could not be delivered from remote threads when p9_mux_poll_stop() from p9_conn_destroy() from p9_fd_close() is called. Therefore, calling set_thread_flag(TIF_SIGPENDING)/recalc_sigpending() every time would be needed if we count on signals for making kernel_read()/kernel_write() non-blocking. Link: https://syzkaller.appspot.com/bug?extid=8b41a1365f1106fd0f33 [1] Reported-by: syzbot Signed-off-by: Tetsuo Handa Tested-by: syzbot Reviewed-by: Christian Schoenebeck --- Although syzbot tested that this patch solves hung task problem, syzbot cannot verify that this patch will not break functionality of p9 users. Please test before applying this patch. net/9p/trans_fd.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index e758978b44be..9870597da583 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -821,11 +821,13 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd) goto out_free_ts; if (!(ts->rd->f_mode & FMODE_READ)) goto out_put_rd; + ts->rd->f_flags |= O_NONBLOCK; ts->wr = fget(wfd); if (!ts->wr) goto out_put_rd; if (!(ts->wr->f_mode & FMODE_WRITE)) goto out_put_wr; + ts->wr->f_flags |= O_NONBLOCK; client->trans = ts; client->status = Connected;