From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp2120.oracle.com ([141.146.126.78]:55946 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727941AbeJFALe (ORCPT ); Fri, 5 Oct 2018 20:11:34 -0400 Date: Fri, 5 Oct 2018 10:11:52 -0700 From: "Darrick J. Wong" Subject: Re: [PATCH 2/2] xfs: fix data corruption w/ unaligned reflink ranges Message-ID: <20181005171152.GU19324@magnolia> References: <20181005012336.1418-1-david@fromorbit.com> <20181005012336.1418-3-david@fromorbit.com> <20181005014014.GO19324@magnolia> <20181005052121.GA12041@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181005052121.GA12041@dastard> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Dave Chinner Cc: linux-xfs@vger.kernel.org On Fri, Oct 05, 2018 at 03:21:21PM +1000, Dave Chinner wrote: > On Thu, Oct 04, 2018 at 06:40:14PM -0700, Darrick J. Wong wrote: > > On Fri, Oct 05, 2018 at 11:23:36AM +1000, Dave Chinner wrote: > > > When reflinking sub-file ranges, a data corruption can occur when > > > the source file range includes a partial EOF block. This shares the > > > unknown data beyond EOF into the second file at a position inside > > > EOF, exposing stale data in the second file. > > > > > > XFS only supports whole block sharing, but we still need to > > > support whole file reflink correctly. Hence if the reflink > > > request includes the last block of the souce file, only proceed with > > > the reflink operation if it lands at or past the destination file's > > > current EOF. If it lands within the destination file EOF, reject the > > > entire request with -EINVAL and make the caller go the hard way. > > > > > > This avoids the data corruption vector, but also avoids disruption > > > of returning EINVAL to userspace for the common case of whole file > > > cloning. > > > > > > Signed-off-by: Dave Chinner > > > --- > > > fs/xfs/xfs_reflink.c | 39 +++++++++++++++++++++++++++++++-------- > > > 1 file changed, 31 insertions(+), 8 deletions(-) > > > > > > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c > > > index 6b0da1b80103..2615271603ce 100644 > > > --- a/fs/xfs/xfs_reflink.c > > > +++ b/fs/xfs/xfs_reflink.c > > > @@ -1229,12 +1229,24 @@ xfs_iolock_two_inodes_and_break_layout( > > > * hence can introduce a corruption into the file that has it's > > > * block replaced. > > > * > > > - * Despite this issue, we still need to report that range as successfully > > > - * deduped to avoid confusing userspace with EINVAL errors on completely > > > - * matching file data. The only time that an unaligned length will be passed to > > > - * us is when it spans the EOF block of the source file, so if we simply mask it > > > - * down to be block aligned here the we will dedupe everything but that partial > > > - * EOF block. > > > + * In similar fashion, the VFS file cloning also allows partial EOF blocks to be > > > + * "block aligned" for the purposes of cloning entire files. > > > + * However, if the source file range > > > + * includes the EOF block and it lands within the existing EOF of the > > > + * destination file, then we can expose stale data from beyond the source file > > > + * EOF in the destination file. > > > + * > > > + * XFs doesn't support partial block sharing, so in both cases we have check > > > + * these cases ourselves. For dedupe, we can simply round the length to dedupe > > > + * down to the previous whole block and ignore the partial EOF block. While this > > > + * means we can't dedupe the last block of a file, this is an acceptible > > > + * tradeoff for simplicity on implementation. > > > + * > > > + * For cloning, we want to share the partial EOF block if it is also the new EOF > > > + * block of the destination file. If the partial EOF blck lies inside the > > > + * existing destination EOF, then we have to abort the clone to avoid exposing > > > + * stale data int eh destination file. Hence we reject these clone attempts with > > > + * -EINVAL in this case. > > > */ > > > int > > > xfs_reflink_remap_range( > > > @@ -1255,6 +1267,7 @@ xfs_reflink_remap_range( > > > xfs_filblks_t fsblen; > > > xfs_extlen_t cowextsize; > > > ssize_t ret; > > > + u64 blkmask = i_blocksize(inode_in) - 1; > > > > > > if (!xfs_sb_version_hasreflink(&mp->m_sb)) > > > return -EOPNOTSUPP; > > > @@ -1292,8 +1305,18 @@ xfs_reflink_remap_range( > > > * from the source file so we don't try to dedupe the partial > > > * EOF block. > > > */ > > > - if (is_dedupe) > > > - len &= ~((u64)i_blocksize(inode_in) - 1); > > > + if (is_dedupe) { > > > + len &= ~blkmask; > > > + } else if (len & blkmask) { > > > + /* > > > + * The user is attempting to share a partial EOF block, > > > + * if it's inside the destination EOF then reject it > > > + */ > > > + if (pos_out + len < i_size_read(inode_out)) { > > > + ret = -EINVAL; > > > + goto out_unlock; > > > > Hmm... to integrate this with the new series I just posted, I think we'd > > decrease len to be block aligned (perhaps in generic_clone_checks) so > > that copy_file_range would be able to pagecache copy the last bit > > instead of failing the whole operation. IOWs, > > > > if (is_dedupe) { > > len &= ~blkmask; > > } else if (len & blkmask) { > > if (pos_out + len < size_out) { > > len &= ~blkmask; > > } > > } > > OK. But if I'm going to push it with just the EOF zeroing and > ctime/suid fixes, then this doesn't change until the handling of > partial completion is added to XFS later in the patchset, right? Right. If you add this series before the partial completion patches I'll fix things up when I rebase that part of my series. --D > Cheers, > > Dave. > > -- > Dave Chinner > david@fromorbit.com