linux-kernel - [PATCH] tty: serial_core: Fix uart_state refcnt leak when the port startup

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Message-Id: <1592052738-95202-1-git-send-email-xiyuyang19@fudan.edu.cn>
Date:   Sat, 13 Jun 2020 20:52:18 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] tty: serial_core: Fix uart_state refcnt leak when the port startup

uart_port_startup() invokes uart_port_lock(), which returns a reference
of the uart_port object if increases the refcount of the uart_state
object successfully or returns NULL if fails.

However, uart_port_startup() don't take the return value of
uart_port_lock() as the new uart_port object to "uport" and use the old
"uport" instead to balance refcount in uart_port_unlock(), which may
cause a redundant decrement of refcount occurred when the new "uport"
equals to NULL and then cause a potential memory leak.

Fix this issue by update the "uport" object to the return value of
uart_port_lock() when invoking uart_port_lock().

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
 drivers/tty/serial/serial_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 57840cf90388..968fd619aec0 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -205,7 +205,7 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 	if (!page)
 		return -ENOMEM;

-	uart_port_lock(state, flags);
+	uport = uart_port_lock(state, flags);
 	if (!state->xmit.buf) {
 		state->xmit.buf = (unsigned char *) page;
 		uart_circ_clear(&state->xmit);
-- 
2.7.4