[PATCH] vt: add mode validation in vt_setactivate

[PATCH] vt: add mode validation in vt_setactivate

[Wang Zihan]

The vt_setactivate() function accepts any mode value without validation,
while VT_SETMODE correctly rejects invalid values (only VT_AUTO and
VT_PROCESS are valid).

This allows users to set invalid mode values (e.g., 0xFF) which bypasses
VT_PROCESS signal handling and causes undefined VT switching behavior.

Fix this by adding the same validation as VT_SETMODE.

Signed-off-by: Wang Zihan <jiyu03@qq.com>
---
 drivers/tty/vt/vt_ioctl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
index 28993a3d0acb..b8787283a0fa 100644
--- a/drivers/tty/vt/vt_ioctl.c
+++ b/drivers/tty/vt/vt_ioctl.c
@@ -596,6 +596,8 @@ static int vt_setactivate(struct vt_setactivate __user *sa)
 		return -EFAULT;
 	if (vsa.console == 0 || vsa.console > MAX_NR_CONSOLES)
 		return -ENXIO;
+	if (vsa.mode.mode != VT_AUTO && vsa.mode.mode != VT_PROCESS)
+		return -EINVAL;
 
 	vsa.console--;
 	vsa.console = array_index_nospec(vsa.console, MAX_NR_CONSOLES);
-- 
2.54.0

Re: [PATCH] vt: add mode validation in vt_setactivate

[Greg KH]

On Sun, May 03, 2026 at 03:46:15AM +0800, Wang Zihan wrote:
> The vt_setactivate() function accepts any mode value without validation,
> while VT_SETMODE correctly rejects invalid values (only VT_AUTO and
> VT_PROCESS are valid).
> 
> This allows users to set invalid mode values (e.g., 0xFF) which bypasses
> VT_PROCESS signal handling and causes undefined VT switching behavior.
> 
> Fix this by adding the same validation as VT_SETMODE.
> 
> Signed-off-by: Wang Zihan <jiyu03@qq.com>
> ---
>  drivers/tty/vt/vt_ioctl.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
> index 28993a3d0acb..b8787283a0fa 100644
> --- a/drivers/tty/vt/vt_ioctl.c
> +++ b/drivers/tty/vt/vt_ioctl.c
> @@ -596,6 +596,8 @@ static int vt_setactivate(struct vt_setactivate __user *sa)
>  		return -EFAULT;
>  	if (vsa.console == 0 || vsa.console > MAX_NR_CONSOLES)
>  		return -ENXIO;
> +	if (vsa.mode.mode != VT_AUTO && vsa.mode.mode != VT_PROCESS)
> +		return -EINVAL;

Are you sure this isn't intentional?  How was this tested?  If an
"invalid" mode is set, what happens?

thanks,

greg k-h

Re: [PATCH] vt: add mode validation in vt_setactivate

[Wang Zihan]

Hi,

I'm writing to follow up on my patch "[PATCH] vt: add mode validation in vt_setactivate" which I sent on May 3, 2026.

Could you please let me know the status of this patch? Is there anything I need to address or update?

Thank you for your time.

Best regards,
Wang Zihan