[PATCH resend 2/5] libata-scsi: fix read-only bits checking in ata_mselect_*()

[tom . ty89]

From: Tom Yan <tom.t...@gmail.com>

Commit 7780081c1f04 ("libata-scsi: Set information sense field for
invalid parameter") changed how ata_mselect_*() make sure read-only
bits are not modified. The new implementation introduced a bug that
the read-only bits in the byte that has a changeable bit will not
be checked.

Added the necessary check, with comments explaining the heuristic.

Signed-off-by: Tom Yan <tom.t...@gmail.com>

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index eb5e8ff..ac90676 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -3631,8 +3631,18 @@ static int ata_mselect_caching(struct ata_queued_cmd *qc,
         */
        ata_msense_caching(dev->id, mpage, false);
        for (i = 0; i < CACHE_MPAGE_LEN - 2; i++) {
-               if (i == 0)
-                       continue;
+               /* Check the first byte */
+               if (i == 0) {
+                       /* except the WCE bit */
+                       if ((mpage[i + 2] & 0xfb) != (buf[i] & 0xfb)) {
+                               *fp = i;
+                               return -EINVAL;
+                       } else {
+                               continue;
+                       }
+               }
+
+               /* Check the remaining bytes */
                if (mpage[i + 2] != buf[i]) {
                        *fp = i;
                        return -EINVAL;
@@ -3686,8 +3696,18 @@ static int ata_mselect_control(struct ata_queued_cmd *qc,
         */
        ata_msense_control(dev, mpage, false);
        for (i = 0; i < CONTROL_MPAGE_LEN - 2; i++) {
-               if (i == 0)
-                       continue;
+               /* Check the first byte */
+               if (i == 0) {
+                       /* except the D_SENSE bit */
+                       if ((mpage[i + 2] & 0xfb) != (buf[i] & 0xfb)) {
+                               *fp = i;
+                               return -EINVAL;
+                       } else {
+                               continue;
+                       }
+               }
+
+               /* Check the remaining bytes */
                if (mpage[2 + i] != buf[i]) {
                        *fp = i;
                        return -EINVAL;
-- 
2.9.0