Re: [PATCH 03/11] xfs: remote attribute read too short

Ben Myers
2013-05-21T20:59:25Z

On Tue, May 21, 2013 at 06:02:02PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Reading a maximally size remote attribute fails when CRCs are
> enabled with this verification error:
>
> XFS (vdb): remote attribute header does not match required off/len/owner)
>
> There are two reasons for this, the first being that the
> length of the buffer being read is determined from the
> args->rmtblkcnt which doesn't take into account CRC headers. Hence
> the mapped length ends up being too short and so we need to
> calculate it directly from the value length.
>
> The second is that the byte count of valid data within a buffer is
> capped by the length of the data and so doesn't take into account
> that the buffer might be longer due to headers. Hence we need to
> calculate the data space in the buffer first before calculating the
> actual byte count of data.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_attr_remote.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/fs/xfs/xfs_attr_remote.c b/fs/xfs/xfs_attr_remote.c
> index aad95b0..bcdc07c 100644
> --- a/fs/xfs/xfs_attr_remote.c
> +++ b/fs/xfs/xfs_attr_remote.c
> @@ -52,9 +52,11 @@ xfs_attr3_rmt_blocks(
> struct xfs_mount *mp,
> int attrlen)
> {
> - int buflen = XFS_ATTR3_RMT_BUF_SPACE(mp,
> - mp->m_sb.sb_blocksize);
> - return (attrlen + buflen - 1) / buflen;
> + if (xfs_sb_version_hascrc(&mp->m_sb)) {
> + int buflen = XFS_ATTR3_RMT_BUF_SPACE(mp, mp->m_sb.sb_blocksize);
> + return (attrlen + buflen - 1) / buflen;
> + }
> + return XFS_B_TO_FSB(mp, attrlen);

xfs_attr_rmtval_set, xfs_attr3_rmt_blocks, and XFS_ATTR3_RMT_BUF_SPACE all have
checks for crcs on the superblock. It's like I'm seeing stars.

> }
>
> static bool
> @@ -206,8 +208,9 @@ xfs_attr_rmtval_get(
>
> while (valuelen > 0) {
> nmap = ATTR_RMTVALUE_MAPSIZE;
> + blkcnt = xfs_attr3_rmt_blocks(mp, valuelen);
> error = xfs_bmapi_read(args->dp, (xfs_fileoff_t)lblkno,
> - args->rmtblkcnt, map, &nmap,
> + blkcnt, map, &nmap,

Isn't blkcnt wrong on the 2nd or greater iteration of this loop? Looks like an old bug.

> XFS_BMAPI_ATTRFORK);
> if (error)
> return error;
> @@ -227,8 +230,8 @@ xfs_attr_rmtval_get(
> if (error)
> return error;
>
> - byte_cnt = min_t(int, valuelen, BBTOB(bp->b_length));
> - byte_cnt = XFS_ATTR3_RMT_BUF_SPACE(mp, byte_cnt);
> + byte_cnt = XFS_ATTR3_RMT_BUF_SPACE(mp, BBTOB(bp->b_length));
> + byte_cnt = min_t(int, valuelen, byte_cnt);

And now byte_cnt reflects the number of bytes in the mapping, less the size of
a header..

Reviewed-by: Ben Myers <bpm@sgi.com>