xfs: Check for extent overflow when moving extent from cow to data fork

mainline inclusion
from mainline-v5.12-rc1
commit 5f1d5bbf
category: bugfix
bugzilla: 187510,https://gitee.com/openeuler/kernel/issues/I4KIAO

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5f1d5bbfb2e674052a9fe542f53678978af20770

--------------------------------

Moving an extent to data fork can cause a sub-interval of an existing
extent to be unmapped. This will increase extent count by 1. Mapping in
the new extent can increase the extent count by 1 again i.e.
 | Old extent | New extent | Old extent |
Hence number of extents increases by 2.
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NAllison Henderson <allison.henderson@oracle.com>
Signed-off-by: NChandan Babu R <chandanrlinux@gmail.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Signed-off-by: NGuo Xuenan <guoxuenan@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/xfs/libxfs/xfs_inode_fork.h

@@ -79,6 +79,15 @@ struct xfs_ifork {
 #define XFS_IEXT_WRITE_UNWRITTEN_CNT	(2)
 
 
+/*
+ * Moving an extent to data fork can cause a sub-interval of an existing extent
+ * to be unmapped. This will increase extent count by 1. Mapping in the new
+ * extent can increase the extent count by 1 again i.e.
+ * | Old extent | New extent | Old extent |
+ * Hence number of extents increases by 2.
+ */
+#define XFS_IEXT_REFLINK_END_COW_CNT	(2)
+
 /*
  * Fork handling.
  */

fs/xfs/xfs_reflink.c

@@ -615,6 +615,11 @@ xfs_reflink_end_cow_extent(
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	xfs_trans_ijoin(tp, ip, 0);
 
+	error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
+			XFS_IEXT_REFLINK_END_COW_CNT);
+	if (error)
+		goto out_cancel;
+
 	/*
 	 * In case of racing, overlapping AIO writes no COW extents might be
 	 * left by the time I/O completes for the loser of the race.  In that