scsi: check the whole result for reading write protect flag

hulk inclusion
category: bugfix
bugzilla: NA
CVE: NA

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

When the scsi device status is offline, mode sense command will return a
result with only DID_NO_CONNECT set. Then in sd_read_write_protect_flag(),
only status byte of the result is checked, we still consider the command
returned good, and read sdkp->write_prot from the buffer. And because of
bug [1], garbage data is copied to the buffer, the disk sometimes
be set readonly. When the scsi device is set running again, users cannot
write data to the disk.

Fix this by check the whole result returned by the driver.

[1] https://patchwork.kernel.org/project/linux-block/patch/20210318122621.330010-1-yanaijie@huawei.com/Signed-off-by: NJason Yan <yanaijie@huawei.com>
Reviewed-by: NYufen Yu <yuyufen@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

drivers/scsi/sd.c

@@ -2651,18 +2651,18 @@ sd_read_write_protect_flag(struct scsi_disk *sdkp, unsigned char *buffer)
 		 * 5: Illegal Request, Sense Code 24: Invalid field in
 		 * CDB.
 		 */
-		if (!scsi_status_is_good(res))
+		if (!scsi_result_is_good(res))
 			res = sd_do_mode_sense(sdp, 0, 0, buffer, 4, &data, NULL);
 
 		/*
 		 * Third attempt: ask 255 bytes, as we did earlier.
 		 */
-		if (!scsi_status_is_good(res))
+		if (!scsi_result_is_good(res))
 			res = sd_do_mode_sense(sdp, 0, 0x3F, buffer, 255,
 					       &data, NULL);
 	}
 
-	if (!scsi_status_is_good(res)) {
+	if (!scsi_result_is_good(res)) {
 		sd_first_printk(KERN_WARNING, sdkp,
 			  "Test WP failed, assume Write Enabled\n");
 	} else {

include/scsi/scsi.h

@@ -55,6 +55,19 @@ static inline int scsi_status_is_good(int status)
 		(status == SAM_STAT_COMMAND_TERMINATED));
 }
 
+/** scsi_result_is_good - check the result return.
+ *
+ * @result: the result passed up from the driver (including host and
+ *          driver components)
+ *
+ * Drivers may only set other bytes but not status byte.
+ * This checks both the status byte and other bytes.
+ */
+static inline int scsi_result_is_good(int result)
+{
+	return scsi_status_is_good(result) && (result & ~0xff) == 0;
+}
+
 
 /*
  * standard mode-select header prepended to all mode-select commands