From patchwork Thu Nov 8 22:19:09 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dave Chinner X-Patchwork-Id: 10675067 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 368B414D6 for ; Thu, 8 Nov 2018 22:19:20 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 280C82E194 for ; Thu, 8 Nov 2018 22:19:20 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1C7302E42E; Thu, 8 Nov 2018 22:19:20 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 99DDD2E40F for ; Thu, 8 Nov 2018 22:19:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731329AbeKIH4w (ORCPT ); Fri, 9 Nov 2018 02:56:52 -0500 Received: from ipmail03.adl2.internode.on.net ([150.101.137.141]:35615 "EHLO ipmail03.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728535AbeKIH4w (ORCPT ); Fri, 9 Nov 2018 02:56:52 -0500 Received: from ppp59-167-129-252.static.internode.on.net (HELO dastard) ([59.167.129.252]) by ipmail03.adl2.internode.on.net with ESMTP; 09 Nov 2018 08:49:15 +1030 Received: from discord.disaster.area ([192.168.1.111]) by dastard with esmtp (Exim 4.80) (envelope-from ) id 1gKsdr-00023m-Of; Fri, 09 Nov 2018 09:19:11 +1100 Received: from dave by discord.disaster.area with local (Exim 4.91) (envelope-from ) id 1gKsdr-0008IT-Nd; Fri, 09 Nov 2018 09:19:11 +1100 From: Dave Chinner To: linux-xfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Subject: [PATCH 2/2] iomap: dio data corruption and spurious errors when pipes fill Date: Fri, 9 Nov 2018 09:19:09 +1100 Message-Id: <20181108221909.27602-3-david@fromorbit.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181108221909.27602-1-david@fromorbit.com> References: <20181108221909.27602-1-david@fromorbit.com> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Dave Chinner When doing direct IO to a pipe for do_splice_direct(), then pipe is trivial to fill up and overflow as it can only hold 16 pages. At this point bio_iov_iter_get_pages() then returns -EFAULT, and we abort the IO submission process. Unfortunately, iomap_dio_rw() propagates the error back up the stack. The error is converted from the EFAULT to EAGAIN in generic_file_splice_read() to tell the splice layers that the pipe is full. do_splice_direct() completely fails to handle EAGAIN errors (it aborts on error) and returns EAGAIN to the caller. copy_file_write() then compeltely fails to handle EAGAIN as well, and so returns EAGAIN to userspace, having failed to copy the data it was asked to. Avoid this whole steaming pile of fail by having iomap_dio_rw() silently swallow EFAULT errors and so do short reads. To make matters worse, iomap_dio_actor() has a stale data exposure bug bio_iov_iter_get_pages() fails - it does not zero the tail block that it may have been left uncovered by partial IO. Fix the error handling case to drop to the sub-block zeroing rather than immmediately returning the -EFAULT error. Signed-off-by: Dave Chinner Reviewed-by: Darrick J. Wong Reviewed-by: Christoph Hellwig --- fs/iomap.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/fs/iomap.c b/fs/iomap.c index 7aacd48c593e..2fda13bc37d8 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -1775,7 +1775,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length, struct bio *bio; bool need_zeroout = false; bool use_fua = false; - int nr_pages, ret; + int nr_pages, ret = 0; size_t copied = 0; if ((pos | length | align) & ((1 << blkbits) - 1)) @@ -1839,8 +1839,14 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length, ret = bio_iov_iter_get_pages(bio, &iter); if (unlikely(ret)) { + /* + * We have to stop part way through an IO. We must fall through + * to the sub-block tail zeroing here, otherwise this + * short IO may expose stale data in the tail of the + * block we haven't written data to. + */ bio_put(bio); - return copied ? copied : ret; + goto zero_tail; } n = bio->bi_iter.bi_size; @@ -1877,6 +1883,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length, * the block tail in the latter case, we can expose stale data via mmap * reads of the EOF block. */ +zero_tail: if (need_zeroout || ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) { /* zero out from the end of the write to the end of the block */ @@ -1884,7 +1891,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length, if (pad) iomap_dio_zero(dio, iomap, pos, fs_block_size - pad); } - return copied; + return copied ? copied : ret; } static loff_t @@ -2079,6 +2086,15 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, dio->wait_for_completion = true; ret = 0; } + + /* + * splicing to pipes can fail on a full pipe. We have to + * swallow this to make it look like a short IO + * otherwise the higher splice layers will completely + * mishandle the error and stop moving data. + */ + if (ret == -EFAULT) + ret = 0; break; } pos += ret;