On Fri, 17 Jan 2014 15:12:05 -0500
Scott Mayhew <smayhew@xxxxxxxxxx> wrote:
> We should always make sure the cached page is up-to-date when we're
> determining whether we can extend a write to cover the full page -- even
> if we've received a write delegation from the server.
>
> Commit c7559663 added logic to skip this check if we have a write
> delegation, which can lead to data corruption such as the following
> scenario if client B receives a write delegation from the NFS server:
>
> Client A:
> # echo 123456789 > /mnt/file
>
> Client B:
> # echo abcdefghi >> /mnt/file
> # cat /mnt/file
> 0�D0�abcdefghi
>
> Just because we hold a write delegation doesn't mean that we've read in
> the entire page contents.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.11+
> Signed-off-by: Scott Mayhew <smayhew@xxxxxxxxxx>
> ---
> fs/nfs/write.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> index c1d5482..6a85038 100644
> --- a/fs/nfs/write.c
> +++ b/fs/nfs/write.c
> @@ -922,19 +922,20 @@ out:
> * extend the write to cover the entire page in order to avoid fragmentation
> * inefficiencies.
> *
> - * If the file is opened for synchronous writes or if we have a write delegation
> - * from the server then we can just skip the rest of the checks.
> + * If the file is opened for synchronous writes then we can just skip the rest
> + * of the checks.
> */
> static int nfs_can_extend_write(struct file *file, struct page *page, struct inode *inode)
> {
> if (file->f_flags & O_DSYNC)
> return 0;
> + if (!nfs_write_pageuptodate(page, inode))
> + return 0;
> if (NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
> return 1;
> - if (nfs_write_pageuptodate(page, inode) && (inode->i_flock == NULL ||
> - (inode->i_flock->fl_start == 0 &&
> + if (inode->i_flock == NULL || (inode->i_flock->fl_start == 0 &&
> inode->i_flock->fl_end == OFFSET_MAX &&
> - inode->i_flock->fl_type != F_RDLCK)))
> + inode->i_flock->fl_type != F_RDLCK))
> return 1;
> return 0;
> }
Makes sense. We can't extend the write unless we know that the page
is uptodate, or we'll potentially be writing uninitialized data.
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
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