linux-kernel - [PATCH v2 1/3] serial: core: Potential overflow of frame

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Message-ID: <20231014181333.2579530-1-vamshigajjela@google.com>
Date:   Sat, 14 Oct 2023 23:43:33 +0530
From:   Vamshi Gajjela <vamshigajjela@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        ilpo.jarvinen@...ux.intel.com
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        manugautam@...gle.com, Subhash Jadavani <sjadavani@...gle.com>,
        Channa Kadabi <kadabi@...gle.com>,
        VAMSHI GAJJELA <vamshigajjela@...gle.com>
Subject: [PATCH v2 1/3] serial: core: Potential overflow of frame_time

From: VAMSHI GAJJELA <vamshigajjela@...gle.com>

uart_update_timeout() sets a u64 value to an unsigned int frame_time.
While it can be cast to u32 before assignment, there's a specific case
where frame_time is cast to u64. Since frame_time consistently
participates in u64 arithmetic, its data type is converted to u64 to
eliminate the need for explicit casting.

Signed-off-by: VAMSHI GAJJELA <vamshigajjela@...gle.com>
---
v2:
- use DIV64_U64_ROUND_UP with frame_time

 drivers/tty/serial/8250/8250_port.c | 2 +-
 include/linux/serial_core.h         | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 141627370aab..d1bf794498c4 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1510,7 +1510,7 @@ static inline void __stop_tx(struct uart_8250_port *p)
 			 * rather than after it is fully sent.
 			 * Roughly estimate 1 extra bit here with / 7.
 			 */
-			stop_delay = p->port.frame_time + DIV_ROUND_UP(p->port.frame_time, 7);
+			stop_delay = p->port.frame_time + DIV64_U64_ROUND_UP(p->port.frame_time, 7);
 		}
 
 		__stop_tx_rs485(p, stop_delay);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index bb6f073bc159..b128513b009a 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -558,7 +558,7 @@ struct uart_port {
 
 	bool			hw_stopped;		/* sw-assisted CTS flow state */
 	unsigned int		mctrl;			/* current modem ctrl settings */
-	unsigned int		frame_time;		/* frame timing in ns */
+	unsigned long		frame_time;		/* frame timing in ns */
 	unsigned int		type;			/* port type */
 	const struct uart_ops	*ops;
 	unsigned int		custom_divisor;
@@ -764,7 +764,7 @@ unsigned int uart_get_divisor(struct uart_port *port, unsigned int baud);
  */
 static inline unsigned long uart_fifo_timeout(struct uart_port *port)
 {
-	u64 fifo_timeout = (u64)READ_ONCE(port->frame_time) * port->fifosize;
+	u64 fifo_timeout = READ_ONCE(port->frame_time) * port->fifosize;
 
 	/* Add .02 seconds of slop */
 	fifo_timeout += 20 * NSEC_PER_MSEC;
-- 
2.42.0.655.g421f12c284-goog