4.9-stable review patch. If anyone has any objections, please let me know.
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From: Brian Foster bfoster@redhat.com
[ Upstream commit 9f2a4505800607e537e9dd9dea4f55c4b0c30c7a ]
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@redhat.com Signed-off-by: Brian Foster bfoster@redhat.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/xfs/xfs_log_recover.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/xfs/xfs_log_recover.c +++ b/fs/xfs/xfs_log_recover.c @@ -753,7 +753,7 @@ 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