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