From 2104eb283df66a482b60254299acbe3c68c03412 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Wed, 7 Apr 2021 12:23:20 +0200
Subject: [PATCH] staging: fwserial: fix TIOCSSERIAL permission check
Git-commit: 2104eb283df66a482b60254299acbe3c68c03412
Patch-mainline: v5.13-rc1
References: git-fixes

Changing the port close-delay parameter is a privileged operation so
make sure to return -EPERM if a regular user tries to change it.

Fixes: 7355ba3445f2 ("staging: fwserial: Add TTY-over-Firewire serial driver")
Cc: stable@vger.kernel.org      # 3.8
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407102334.32361-3-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/staging/fwserial/fwserial.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/fwserial/fwserial.c b/drivers/staging/fwserial/fwserial.c
index c963848522b1..440d11423812 100644
--- a/drivers/staging/fwserial/fwserial.c
+++ b/drivers/staging/fwserial/fwserial.c
@@ -1232,20 +1232,24 @@ static int set_serial_info(struct tty_struct *tty,
 			   struct serial_struct *ss)
 {
 	struct fwtty_port *port = tty->driver_data;
+	unsigned int cdelay;
 
 	if (ss->irq != 0 || ss->port != 0 || ss->custom_divisor != 0 ||
 	    ss->baud_base != 400000000)
 		return -EPERM;
 
+	cdelay = msecs_to_jiffies(ss->close_delay * 10);
+
 	mutex_lock(&port->port.mutex);
 	if (!capable(CAP_SYS_ADMIN)) {
-		if (((ss->flags & ~ASYNC_USR_MASK) !=
+		if (cdelay != port->port.close_delay ||
+		    ((ss->flags & ~ASYNC_USR_MASK) !=
 		     (port->port.flags & ~ASYNC_USR_MASK))) {
 			mutex_unlock(&port->port.mutex);
 			return -EPERM;
 		}
 	}
-	port->port.close_delay = msecs_to_jiffies(ss->close_delay * 10);
+	port->port.close_delay = cdelay;
 	mutex_unlock(&port->port.mutex);
 
 	return 0;
-- 
2.26.2