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

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Message-ID: <20231014104942.856152-2-vamshigajjela@google.com>
Date:   Sat, 14 Oct 2023 16:19:40 +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 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>
---
 include/linux/serial_core.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

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