[PATCH 5.17 0713/1126] mxser: fix xmit_buf leak in activate when LSR == 0xff

[Greg Kroah-Hartman]

From: Jiri Slaby <jslaby@xxxxxxx>

[ Upstream commit cd3a4907ee334b40d7aa880c7ab310b154fd5cd4 ]

When LSR is 0xff in ->activate() (rather unlike), we return an error.
Provided ->shutdown() is not called when ->activate() fails, nothing
actually frees the buffer in this case.

Fix this by properly freeing the buffer in a designated label. We jump
there also from the "!info->type" if now too.

Fixes: 6769140d3047 ("tty: mxser: use the tty_port_open method")
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Link: https://lore.kernel.org/r/20220124071430.14907-6-jslaby@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/tty/mxser.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c
index c858aff721c4..fbb796f83753 100644
--- a/drivers/tty/mxser.c
+++ b/drivers/tty/mxser.c
@@ -744,6 +744,7 @@ static int mxser_activate(struct tty_port *port, struct tty_struct *tty)
 	struct mxser_port *info = container_of(port, struct mxser_port, port);
 	unsigned long page;
 	unsigned long flags;
+	int ret;
 
 	page = __get_free_page(GFP_KERNEL);
 	if (!page)
@@ -753,9 +754,9 @@ static int mxser_activate(struct tty_port *port, struct tty_struct *tty)
 
 	if (!info->type) {
 		set_bit(TTY_IO_ERROR, &tty->flags);
-		free_page(page);
 		spin_unlock_irqrestore(&info->slock, flags);
-		return 0;
+		ret = 0;
+		goto err_free_xmit;
 	}
 	info->port.xmit_buf = (unsigned char *) page;
 
@@ -775,8 +776,10 @@ static int mxser_activate(struct tty_port *port, struct tty_struct *tty)
 		if (capable(CAP_SYS_ADMIN)) {
 			set_bit(TTY_IO_ERROR, &tty->flags);
 			return 0;
-		} else
-			return -ENODEV;
+		}
+
+		ret = -ENODEV;
+		goto err_free_xmit;
 	}
 
 	/*
@@ -821,6 +824,10 @@ static int mxser_activate(struct tty_port *port, struct tty_struct *tty)
 	spin_unlock_irqrestore(&info->slock, flags);
 
 	return 0;
+err_free_xmit:
+	free_page(page);
+	info->port.xmit_buf = NULL;
+	return ret;
 }
 
 /*
-- 
2.34.1