esas2r: Fix array overrun

Check the array size *before* dereferencing it with a user provided
offset.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/esas2r/esas2r_ioctl.c

@@ -1360,14 +1360,15 @@ int esas2r_ioctl_handler(void *hostdata, int cmd, void __user *arg)
 	if (ioctl->header.channel == 0xFF) {
 		a = (struct esas2r_adapter *)hostdata;
 	} else {
-		a = esas2r_adapters[ioctl->header.channel];
-		if (ioctl->header.channel >= MAX_ADAPTERS || (a == NULL)) {
+		if (ioctl->header.channel >= MAX_ADAPTERS ||
+			esas2r_adapters[ioctl->header.channel] == NULL) {
 			ioctl->header.return_code = IOCTL_BAD_CHANNEL;
 			esas2r_log(ESAS2R_LOG_WARN, "bad channel value");
 			kfree(ioctl);
 
 			return -ENOTSUPP;
 		}
+		a = esas2r_adapters[ioctl->header.channel];
 	}
 
 	switch (cmd) {