linux-kernel - Re: [PATCH] scsi: Fix a use after free in st

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Date:   Thu, 11 Mar 2021 20:10:18 +0200
From:   "Kai Mäkisara (Kolumbus)" 
        <kai.makisara@...umbus.fi>
To:     Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Cc:     "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: Fix a use after free in st_open



> On 11. Mar 2021, at 8.46, Lv Yunlong <lyl2019@...l.ustc.edu.cn> wrote:
> 
> 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().
> 
> Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>

Acked-by: Kai Mäkisara <kai.makisara@...umbus.fi>

> ---
> 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 841ad2fc369a..9ca536aae784 100644
> --- a/drivers/scsi/st.c
> +++ b/drivers/scsi/st.c
> @@ -1269,8 +1269,8 @@ 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);
> 	}

Potential problem only when debugging enabled, but should be fixed.

Thanks,
Kai