[PATCH] scsi: Fix a use after free in st_open

[PATCH] scsi: Fix a use after free in st_open

[Lv Yunlong]

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@mail.ustc.edu.cn>
---
 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);
 	}
 
-- 
2.25.1

Re: [PATCH] scsi: Fix a use after free in st_open

["Kai Mäkisara (Kolumbus)"]

> On 11. Mar 2021, at 8.46, Lv Yunlong <lyl2019@mail.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@mail.ustc.edu.cn>

Acked-by: Kai Mäkisara <kai.makisara@kolumbus.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

Re: [PATCH] scsi: Fix a use after free in st_open

[Martin K. Petersen]

On Wed, 10 Mar 2021 22:46:36 -0800, Lv Yunlong 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().

Applied to 5.12/scsi-fixes, thanks!

[1/1] scsi: Fix a use after free in st_open
      https://git.kernel.org/mkp/scsi/c/c8c165dea4c8

-- 
Martin K. Petersen	Oracle Linux Engineering