[PATCH] CDROM_SEND_PACKET bug

I just found Yet Another Bug in scsi_ioctl - CDROM_SEND_PACKET puts a
kernel pointer in hdr->cmdp, where sg_io() expects to find user address.
This worked up until recently because of the memcpy bug, but now it
doesn't because we do the proper copy_from_user(). 

This fix undoes the user copy code from sg_io, and instead makes the
SG_IO ioctl copy it locally.  This makes SG_IO and CDROM_SEND_PACKET
agree on the calling convention, and everybody is happy. 

I've tested that both

   cdrecord -dev=/dev/hdc -inq

and

   cdrecord -dev=ATAPI:/dev/hdc -inq

works now.  The former will use SG_IO, the latter CDROM_SEND_PACKET (and
incidentally would work in both 2.4 and 2.6, if it wasn't for
CDROM_SEND_PACKET sucking badly in 2.4).

drivers/block/scsi_ioctl.c

@@ -150,7 +150,6 @@ static int sg_io(request_queue_t *q, struct block_device *bdev,
 	struct request *rq;
 	struct bio *bio;
 	char sense[SCSI_SENSE_BUFFERSIZE];
-	unsigned char cdb[BLK_MAX_CDB];
 	void *buffer;
 
 	if (hdr->interface_id != 'S')
@@ -167,9 +166,6 @@ static int sg_io(request_queue_t *q, struct block_device *bdev,
 	if (hdr->dxfer_len > (q->max_sectors << 9))
 		return -EIO;
 
-	if (copy_from_user(cdb, hdr->cmdp, hdr->cmd_len))
-		return -EFAULT;
-
 	reading = writing = 0;
 	buffer = NULL;
 	bio = NULL;
@@ -220,7 +216,7 @@ static int sg_io(request_queue_t *q, struct block_device *bdev,
 	 * fill in request structure
 	 */
 	rq->cmd_len = hdr->cmd_len;
-	memcpy(rq->cmd, cdb, hdr->cmd_len);
+	memcpy(rq->cmd, hdr->cmdp, hdr->cmd_len);
 	if (sizeof(rq->cmd) != hdr->cmd_len)
 		memset(rq->cmd + hdr->cmd_len, 0, sizeof(rq->cmd) - hdr->cmd_len);
 
@@ -436,12 +432,23 @@ int scsi_cmd_ioctl(struct block_device *bdev, unsigned int cmd, unsigned long ar
 			break;
 		case SG_IO: {
 			struct sg_io_hdr hdr;
+			unsigned char cdb[BLK_MAX_CDB], *old_cdb;
 
-			if (copy_from_user(&hdr, (struct sg_io_hdr *) arg, sizeof(hdr))) {
-				err = -EFAULT;
+			err = -EFAULT;
+			if (copy_from_user(&hdr, (struct sg_io_hdr *) arg, sizeof(hdr)))
 				break;
-			}
+			err = -EINVAL;
+			if (hdr.cmd_len > sizeof(rq->cmd))
+				break;
+			err = -EFAULT;
+			if (copy_from_user(cdb, hdr.cmdp, hdr.cmd_len))
+				break;
+
+			old_cdb = hdr.cmdp;
+			hdr.cmdp = cdb;
 			err = sg_io(q, bdev, &hdr);
+
+			hdr.cmdp = old_cdb;
 			if (copy_to_user((struct sg_io_hdr *) arg, &hdr, sizeof(hdr)))
 				err = -EFAULT;
 			break;