Patch "xfs: fix log block underflow during recovery cycle verification" has been added to the 4.9-stable tree

Patch "xfs: fix log block underflow during recovery cycle verification" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    xfs: fix log block underflow during recovery cycle verification

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     xfs-fix-log-block-underflow-during-recovery-cycle-verification.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Mon Dec 18 14:12:35 CET 2017
From: Brian Foster <bfoster@redhat.com>
Date: Thu, 26 Oct 2017 09:31:16 -0700
Subject: xfs: fix log block underflow during recovery cycle verification

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


Patches currently in stable-queue which might be from bfoster@redhat.com are

queue-4.9/xfs-fix-incorrect-extent-state-in-xfs_bmap_add_extent_unwritten_real.patch
queue-4.9/xfs-fix-log-block-underflow-during-recovery-cycle-verification.patch
queue-4.9/xfs-truncate-pagecache-before-writeback-in-xfs_setattr_size.patch