[PATCH 4.19 15/56] scsi: st: Fix a use after free in st_open()

[Greg Kroah-Hartman]

From: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>

[ Upstream commit c8c165dea4c8f5ad67b1240861e4f6c5395fa4ac ]

In st_open(), if STp->in_use is true, STp will be freed by
scsi_tape_put(). However, STp is still used by DEBC_printk() after. It is
better to DEBC_printk() before scsi_tape_put().

Link: https://lore.kernel.org/r/20210311064636.10522-1-lyl2019@xxxxxxxxxxxxxxxx
Acked-by: Kai Mäkisara <kai.makisara@xxxxxxxxxxx>
Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/scsi/st.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 307df2fa39a3..5078db7743cd 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -1265,8 +1265,8 @@ static int st_open(struct inode *inode, struct file *filp)
 	spin_lock(&st_use_lock);
 	if (STp->in_use) {
 		spin_unlock(&st_use_lock);
-		scsi_tape_put(STp);
 		DEBC_printk(STp, "Device already in use.\n");
+		scsi_tape_put(STp);
 		return (-EBUSY);
 	}
 
-- 
2.30.1