[PATCH 6.1.y 5.15.y 5.10.y] serial: protect uart_port_dtr_rts() in uart_shutdown() too

[Tomas Krcka <tomas.krcka@gmail.com>]

From: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>

[ Upstream commit 602babaa84d627923713acaf5f7e9a4369e77473 ]

Commit af224ca2df29 (serial: core: Prevent unsafe uart port access, part
3) added few uport == NULL checks. It added one to uart_shutdown(), so
the commit assumes, uport can be NULL in there. But right after that
protection, there is an unprotected "uart_port_dtr_rts(uport, false);"
call. That is invoked only if HUPCL is set, so I assume that is the
reason why we do not see lots of these reports.

Or it cannot be NULL at this point at all for some reason :P.

Until the above is investigated, stay on the safe side and move this
dereference to the if too.

I got this inconsistency from Coverity under CID 1585130. Thanks.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240805102046.307511-3-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Adapted over commit 5701cb8bf50e ("tty: Call ->dtr_rts() parameter
active consistently") not in the tree]
Signed-off-by: Tomas Krcka <krckatom@amazon.de>
---
 drivers/tty/serial/serial_core.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 58e857fb8dee..fd9f635dc247 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -339,14 +339,16 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 		/*
 		 * Turn off DTR and RTS early.
 		 */
-		if (uport && uart_console(uport) && tty) {
-			uport->cons->cflag = tty->termios.c_cflag;
-			uport->cons->ispeed = tty->termios.c_ispeed;
-			uport->cons->ospeed = tty->termios.c_ospeed;
-		}
+		if (uport) {
+			if (uart_console(uport) && tty) {
+				uport->cons->cflag = tty->termios.c_cflag;
+				uport->cons->ispeed = tty->termios.c_ispeed;
+				uport->cons->ospeed = tty->termios.c_ospeed;
+			}
 
-		if (!tty || C_HUPCL(tty))
-			uart_port_dtr_rts(uport, 0);
+			if (!tty || C_HUPCL(tty))
+				uart_port_dtr_rts(uport, 0);
+		}
 
 		uart_port_shutdown(port);
 	}
-- 
2.40.1