target: Fix inconsistent address passed to kunmap_atomic() in sbc_dif_copy_prot()

In sbc_dif_copy_prot(), the addresses passed to kunmap_atomic() are
inconsistent with the addresses which are mapped by kmap_atomic().
That could be problematic if an SG element has its length larger than
PAGE_SIZE as kunmap_atomic() will attempt to unmap different page.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: target-devel@vger.kernel.org
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_sbc.c

@@ -1300,13 +1300,14 @@ void sbc_dif_copy_prot(struct se_cmd *cmd, unsigned int sectors, bool read,
 			copied += len;
 			psg_len -= len;
 
+			kunmap_atomic(addr - sg->offset - offset);
+
 			if (offset >= sg->length) {
 				sg = sg_next(sg);
 				offset = 0;
 			}
-			kunmap_atomic(addr);
 		}
-		kunmap_atomic(paddr);
+		kunmap_atomic(paddr - psg->offset);
 	}
 }
 EXPORT_SYMBOL(sbc_dif_copy_prot);