On Mon, Oct 23, 2017 at 10:46:44AM -0400, Brian Foster wrote:
> Unfortunately it is possible for mkfs to format very small
> filesystems with too small of an internal log with respect to the
> various minimum size and block count requirements. If this occurs
> when the log happens to be smaller than the scan window used for
> cycle verification and the scan wraps the end of the log, the
> start_blk calculation in xlog_find_head() underflows and leads to an
> attempt to scan an invalid range of log blocks. This results in log
> recovery failure and a failed mount.
>
> Since there may be filesystems out in the wild with this kind of
> geometry, we cannot simply refuse to mount. Instead, cap the scan
> window for cycle verification to the size of the physical log. This
> ensures that the cycle verification proceeds as expected when the
> scan wraps the end of the log.
>
> Reported-by: Zorro Lang <zlang@xxxxxxxxxx>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
> fs/xfs/xfs_log_recover.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index 80b37a2..019de58 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -760,7 +760,7 @@ xlog_find_head(
> * in the in-core log. The following number can be made tighter if
> * we actually look at the block size of the filesystem.
> */
> - num_scan_bblks = XLOG_TOTAL_REC_SHIFT(log);
> + num_scan_bblks = min_t(int, log_bbnum, XLOG_TOTAL_REC_SHIFT(log));
> if (head_blk >= num_scan_bblks) {
> /*
> * We are guaranteed that the entire check can be performed
> --
> 2.9.5
>
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