xfs: ubsan fixes

Fix some complaints from the UBSAN about signed integer addition overflows.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/xfs_aops.c

@@ -399,7 +399,7 @@ xfs_map_blocks(
 	       (ip->i_df.if_flags & XFS_IFEXTENTS));
 	ASSERT(offset <= mp->m_super->s_maxbytes);
 
-	if (offset + count > mp->m_super->s_maxbytes)
+	if ((xfs_ufsize_t)offset + count > mp->m_super->s_maxbytes)
 		count = mp->m_super->s_maxbytes - offset;
 	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
 	offset_fsb = XFS_B_TO_FSBT(mp, offset);
@@ -1265,7 +1265,7 @@ xfs_map_trim_size(
 	if (mapping_size > size)
 		mapping_size = size;
 	if (offset < i_size_read(inode) &&
-	    offset + mapping_size >= i_size_read(inode)) {
+	    (xfs_ufsize_t)offset + mapping_size >= i_size_read(inode)) {
 		/* limit mapping to block that spans EOF */
 		mapping_size = roundup_64(i_size_read(inode) - offset,
 					  i_blocksize(inode));
@@ -1312,7 +1312,7 @@ xfs_get_blocks(
 	lockmode = xfs_ilock_data_map_shared(ip);
 
 	ASSERT(offset <= mp->m_super->s_maxbytes);
-	if (offset + size > mp->m_super->s_maxbytes)
+	if ((xfs_ufsize_t)offset + size > mp->m_super->s_maxbytes)
 		size = mp->m_super->s_maxbytes - offset;
 	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + size);
 	offset_fsb = XFS_B_TO_FSBT(mp, offset);