scsi: st: Don't modify unknown block number in MTIOCGET

jira LE-2289
Rebuild_History Non-Buildable kernel-4.18.0-553.36.1.el8_10
commit-author Kai Mäkisara <[email protected]>
commit 5bb2d61

Struct mtget field mt_blkno -1 means it is unknown. Don't add anything to
it.

	Signed-off-by: Kai Mäkisara <[email protected]>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=219419#c14
Link: https://lore.kernel.org/r/[email protected]
	Reviewed-by: John Meneghini <[email protected]>
	Tested-by: John Meneghini <[email protected]>
	Signed-off-by: Martin K. Petersen <[email protected]>
(cherry picked from commit 5bb2d61)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

drivers/scsi/st.c

@@ -3755,7 +3755,7 @@ static long st_ioctl(struct file *file, unsigned int cmd_in, unsigned long arg)
 		    ((STp->density << MT_ST_DENSITY_SHIFT) & MT_ST_DENSITY_MASK);
 		mt_status.mt_blkno = STps->drv_block;
 		mt_status.mt_fileno = STps->drv_file;
-		if (STp->block_size != 0) {
+		if (STp->block_size != 0 && mt_status.mt_blkno >= 0) {
 			if (STps->rw == ST_WRITING)
 				mt_status.mt_blkno +=
 				    (STp->buffer)->buffer_bytes / STp->block_size;