From mboxrd@z Thu Jan 1 00:00:00 1970 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 6E905C433FE for ; Tue, 18 Oct 2022 00:17:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231960AbiJRARQ (ORCPT ); Mon, 17 Oct 2022 20:17:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231846AbiJRAOc (ORCPT ); Mon, 17 Oct 2022 20:14:32 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1E8E189CE8; Mon, 17 Oct 2022 17:11:49 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 5A2E6B81B62; Tue, 18 Oct 2022 00:11:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FE21C433B5; Tue, 18 Oct 2022 00:11:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666051906; bh=2lkXz49jQAZ87PnL2dBuQavwTxWiDifoGRhYhQlz6nY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bVBlMwIKJY3/xV/S7vqsQxEwmVf+jc6uQ2UCbw6xjH+AqjMOh2JFuKfe80aJlpn8u peHJClhCMWESxrqOF/VjdYvC7SK5n+4tDLmyS5MaFphMdEe5me3t2cjaiOFdIR1fiT Edwrpw5xHsl7d378DlcSqucZfffcxdxuadWkbbwWYp7lqv+mKPXyruxiBuELgI+VwG znE8JmESz+ssCQ4GbpXLOWr+rVZgmgtH128cKN9ZnZeBwdUuMzC1AbbSbeDmOxGBCy vZROpbxXglMljkIxO8hQpReEScHIJVoaJwRVarRICovtRrjv8Tp1j23/wmmwWF9iMw Ed4pHLg8f0BjA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Tetsuo Handa , syzbot , Christian Schoenebeck , Dominique Martinet , Sasha Levin , ericvh@gmail.com, lucho@ionkov.net, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, v9fs-developer@lists.sourceforge.net, netdev@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 09/10] 9p/trans_fd: always use O_NONBLOCK read/write Date: Mon, 17 Oct 2022 20:11:27 -0400 Message-Id: <20221018001128.2732162-9-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20221018001128.2732162-1-sashal@kernel.org> References: <20221018001128.2732162-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tetsuo Handa [ Upstream commit ef575281b21e9a34dfae544a187c6aac2ae424a9 ] 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://lkml.kernel.org/r/345de429-a88b-7097-d177-adecf9fed342@I-love.SAKURA.ne.jp Link: https://syzkaller.appspot.com/bug?extid=8b41a1365f1106fd0f33 [1] Reported-by: syzbot Signed-off-by: Tetsuo Handa Tested-by: syzbot Reviewed-by: Christian Schoenebeck [Dominique: add comment at Christian's suggestion] Signed-off-by: Dominique Martinet Signed-off-by: Sasha Levin --- net/9p/trans_fd.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index 7d68b4a63997..7194ffa58d3e 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -836,11 +836,14 @@ 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; + /* prevent workers from hanging on IO when fd is a pipe */ + 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; -- 2.35.1