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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        =?UTF-8?q?Kai=20M=C3=A4kisara?= <kai.makisara@kolumbus.fi>,
        Lv Yunlong <lyl2019@mail.ustc.edu.cn>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 22/74] scsi: st: Fix a use after free in st_open()
Date:   Mon,  5 Apr 2021 10:53:46 +0200
Message-Id: <20210405085025.440284067@linuxfoundation.org>
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From: Lv Yunlong <lyl2019@mail.ustc.edu.cn>

[ 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@mail.ustc.edu.cn
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 e3266a64a477..2121e44c342f 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -1267,8 +1267,8 @@ 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