From: Brian Foster Date: Thu, 26 Oct 2017 16:31:16 +0000 (-0700) Subject: xfs: fix log block underflow during recovery cycle verification X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=9f2a4505800607e537e9dd9dea4f55c4b0c30c7a;p=linux.git xfs: fix log block underflow during recovery cycle verification 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 Signed-off-by: Brian Foster Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong --- diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c index 89ce1926a0212..f809deee53a89 100644 --- a/fs/xfs/xfs_log_recover.c +++ b/fs/xfs/xfs_log_recover.c @@ -763,7 +763,7 @@ 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