xfs: Check for extent overflow when remapping an extent

mainline inclusion
from mainline-v5.12-rc1
commit ee898d78
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=ee898d78c3540b44270a5fdffe208d7bbb219d93

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

Remapping an extent involves unmapping the existing extent and mapping
in the new extent. When unmapping, an extent containing the entire unmap
range can be split into two extents,
i.e. | Old extent | hole | Old extent |
Hence extent count increases by 1.

Mapping in the new extent into the destination file can increase the
extent count by 1.
Reviewed-by: NAllison Henderson <allison.henderson@oracle.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@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/xfs_reflink.c

@@ -997,6 +997,7 @@ xfs_reflink_remap_extent(
 	bool			quota_reserved = true;
 	bool			smap_real;
 	bool			dmap_written = xfs_bmap_is_written_extent(dmap);
+	int			iext_delta = 0;
 	int			nimaps;
 	int			error;
 
@@ -1107,6 +1108,16 @@ xfs_reflink_remap_extent(
 			goto out_cancel;
 	}
 
+	if (smap_real)
+		++iext_delta;
+
+	if (dmap_written)
+		++iext_delta;
+
+	error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK, iext_delta);
+	if (error)
+		goto out_cancel;
+
 	if (smap_real) {
 		/*
 		 * If the extent we're unmapping is backed by storage (written