From patchwork Mon Feb 22 12:13:19 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 386221 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, URIBL_RED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4515AC433E0 for ; Mon, 22 Feb 2021 12:16:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E84C464F17 for ; Mon, 22 Feb 2021 12:16:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230438AbhBVMQZ (ORCPT ); Mon, 22 Feb 2021 07:16:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:44936 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230389AbhBVMPp (ORCPT ); Mon, 22 Feb 2021 07:15:45 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7EED264F14; Mon, 22 Feb 2021 12:14:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1613996090; bh=ClW5u69acfm/AsqAy0Vj0bV5RxkRJnX2Eb5Z7iXlRPY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SUcgFLOiDdNHXduSINCgyf7160gqfj9B9b3Ed/HFHe6rTJGyLpuSlEtRfqanrOdEq 6YeYJ8F9ggzRpEdaZ4r4RZi47HeEq6JMjyzH/8Xgt/O6QXshsEVzd2smJjn9VqmK/8 PFoP461G6m35ECTYD8JlXqvWPhffjMOiO6RbkzP8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+3d2c27c2b7dc2a94814d@syzkaller.appspotmail.com, Linus Torvalds , Al Viro Subject: [PATCH 5.10 25/29] tty: protect tty_write from odd low-level tty disciplines Date: Mon, 22 Feb 2021 13:13:19 +0100 Message-Id: <20210222121025.239340563@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210222121019.444399883@linuxfoundation.org> References: <20210222121019.444399883@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Linus Torvalds commit 3342ff2698e9720f4040cc458a2744b2b32f5c3a upstream. Al root-caused a new warning from syzbot to the ttyprintk tty driver returning a write count larger than the data the tty layer actually gave it. Which confused the tty write code mightily, and with the new iov_iter based code, caused a WARNING in iov_iter_revert(). syzbot correctly bisected the source of the new warning to commit 9bb48c82aced ("tty: implement write_iter"), but the oddity goes back much further, it just didn't get caught by anything before. Reported-by: syzbot+3d2c27c2b7dc2a94814d@syzkaller.appspotmail.com Fixes: 9bb48c82aced ("tty: implement write_iter") Debugged-by: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -963,11 +963,14 @@ static inline ssize_t do_tty_write( if (ret <= 0) break; + written += ret; + if (ret > size) + break; + /* FIXME! Have Al check this! */ if (ret != size) iov_iter_revert(from, size-ret); - written += ret; count -= ret; if (!count) break;