scsi: sd: Fix interpretation of VPD B9h length

Fixing the interpretation of the length of the B9h VPD page (Concurrent
Positioning Ranges). Adding 4 is necessary as the first 4 bytes of the page
is the header with page number and length information.  Adding 3 was likely
a misinterpretation of the SBC-5 specification which sets all offsets
starting at zero.

This fixes the error in dmesg:

[ 9.014456] sd 1:0:0:0: [sda] Invalid Concurrent Positioning Ranges VPD page

Link: https://lore.kernel.org/r/[email protected]
Fixes: e815d36 ("scsi: sd: add concurrent positioning ranges support")
Cc: [email protected]
Tested-by: Michael English <[email protected]>
Reviewed-by: Muhammad Ahmad <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Tyler Erickson <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

drivers/scsi/sd.c

@@ -3072,7 +3072,7 @@ static void sd_read_cpr(struct scsi_disk *sdkp)
 		goto out;
 
 	/* We must have at least a 64B header and one 32B range descriptor */
-	vpd_len = get_unaligned_be16(&buffer[2]) + 3;
+	vpd_len = get_unaligned_be16(&buffer[2]) + 4;
 	if (vpd_len > buf_len || vpd_len < 64 + 32 || (vpd_len & 31)) {
 		sd_printk(KERN_ERR, sdkp,
 			  "Invalid Concurrent Positioning Ranges VPD page\n");