scsi: sg: check for valid direction before starting the request

Check for a valid direction before starting the request, otherwise we
risk running into an assertion in the scsi midlayer checking for valid
requests.

[mkp: fixed typo]
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Link: http://www.spinics.net/lists/linux-scsi/msg104400.htmlReported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Hannes Reinecke <hare@suse.com>
Tested-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sg.c

@@ -663,8 +663,6 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 	 * is a non-zero input_size, so emit a warning.
 	 */
 	if (hp->dxfer_direction == SG_DXFER_TO_FROM_DEV) {
-		static char cmd[TASK_COMM_LEN];
-		if (strcmp(current->comm, cmd)) {
 		printk_ratelimited(KERN_WARNING
 				   "sg_write: data in/out %d/%d bytes "
 				   "for SCSI command 0x%x-- guessing "
@@ -673,8 +671,6 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 				   old_hdr.reply_len - (int)SZ_SG_HEADER,
 				   input_size, (unsigned int) cmnd[0],
 				   current->comm);
-			strcpy(cmd, current->comm);
-		}
 	}
 	k = sg_common_write(sfp, srp, cmnd, sfp->timeout, blocking);
 	return (k < 0) ? k : count;
@@ -753,6 +749,29 @@ sg_new_write(Sg_fd *sfp, struct file *file, const char __user *buf,
 	return count;
 }
 
+static bool sg_is_valid_dxfer(sg_io_hdr_t *hp)
+{
+	switch (hp->dxfer_direction) {
+	case SG_DXFER_NONE:
+		if (hp->dxferp || hp->dxfer_len > 0)
+			return false;
+		return true;
+	case SG_DXFER_TO_DEV:
+	case SG_DXFER_FROM_DEV:
+	case SG_DXFER_TO_FROM_DEV:
+		if (!hp->dxferp || hp->dxfer_len == 0)
+			return false;
+		return true;
+	case SG_DXFER_UNKNOWN:
+		if ((!hp->dxferp && hp->dxfer_len) ||
+		    (hp->dxferp && hp->dxfer_len == 0))
+			return false;
+		return true;
+	default:
+		return false;
+	}
+}
+
 static int
 sg_common_write(Sg_fd * sfp, Sg_request * srp,
 		unsigned char *cmnd, int timeout, int blocking)
@@ -773,6 +792,9 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
 			"sg_common_write:  scsi opcode=0x%02x, cmd_size=%d\n",
 			(int) cmnd[0], (int) hp->cmd_len));
 
+	if (!sg_is_valid_dxfer(hp))
+		return -EINVAL;
+
 	k = sg_start_req(srp, cmnd);
 	if (k) {
 		SCSI_LOG_TIMEOUT(1, sg_printk(KERN_INFO, sfp->parentdp,