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 <dchinner@xxxxxxxxxx>
> > > ---
> > > 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@xxxxxxxxxxxxx
