linux-kernel - [PATCH AUTOSEL 6.6 40/58] serial: protect uart_port_dtr_rts() in uart

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Message-ID: <20241004182503.3672477-40-sashal@kernel.org>
Date: Fri,  4 Oct 2024 14:24:13 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sasha Levin <sashal@...nel.org>,
	tony.lindgren@...ux.intel.com,
	andriy.shevchenko@...ux.intel.com,
	ilpo.jarvinen@...ux.intel.com,
	l.sanfilippo@...bus.com,
	pcc@...gle.com,
	linux-serial@...r.kernel.org
Subject: [PATCH AUTOSEL 6.6 40/58] serial: protect uart_port_dtr_rts() in uart_shutdown() too

From: "Jiri Slaby (SUSE)" <jirislaby@...nel.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@...nel.org>
Cc: Peter Hurley <peter@...leysoftware.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Link: https://lore.kernel.org/r/20240805102046.307511-3-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 ed8798fdf522a..d7c59d690a74d 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -374,14 +374,16 @@ 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, false);
+			if (!tty || C_HUPCL(tty))
+				uart_port_dtr_rts(uport, false);
+		}
 
 		uart_port_shutdown(port);
 	}
-- 
2.43.0