scsi: target: tcmu: Allocate zeroed pages for data area

Tcmu populates the data area (used for communication with userspace) with
pages that are allocated by calling alloc_page(GFP_NOIO).  Therefore
previous content of the allocated pages is exposed to user space. Avoid
this by adding __GFP_ZERO flag.

Zeroing the pages does (nearly) not affect tcmu throughput, because
allocated pages are re-used for the data transfers of later SCSI cmds.

Link: https://lore.kernel.org/r/20211013171606.25197-1-bostroesser@gmail.comSigned-off-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_user.c

@@ -523,8 +523,8 @@ static inline int tcmu_get_empty_block(struct tcmu_dev *udev,
 	rcu_read_unlock();
 
 	for (i = cnt; i < page_cnt; i++) {
-		/* try to get new page from the mm */
-		page = alloc_page(GFP_NOIO);
+		/* try to get new zeroed page from the mm */
+		page = alloc_page(GFP_NOIO | __GFP_ZERO);
 		if (!page)
 			break;