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[34.82.187.25]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2e2e5c1b3d7sm6751925ad.70.2026.09.30.05.59.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Sep 2026 05:59:04 -0700 (PDT) From: Hui Peng To: Greg Kroah-Hartman , Jiri Slaby , John Ogness , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Cc: Andy Shevchenko , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Hui Peng Subject: [PATCH v7 2/2] serial: core: reject baud_base values that overflow port->uartclk in uart_set_info() Date: Wed, 30 Sep 2026 12:59:01 +0000 Message-ID: <20260930125901.778868-3-benquike@gmail.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog In-Reply-To: <20260930125901.778868-1-benquike@gmail.com> References: <20260930125901.778868-1-benquike@gmail.com> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In uart_set_info(), new_info->baud_base is multiplied by 16 and stored in uport->uartclk (an unsigned int): uport->uartclk = new_info->baud_base * 16; While uart_set_info() checks if (uartclk == 0) and if (new_info->baud_base < 9600), when new_info->baud_base exceeds UINT_MAX / 16 with low bits set (for example, 0x10000001), multiplying by 16 wraps around in 32-bit unsigned arithmetic to a small non-zero value (16), bypassing both uartclk == 0 and new_info->baud_base < 9600 and setting uport->uartclk = 16 (baud_base = 1, well below the required minimum of 9600 * 16). Use check_mul_overflow(new_info->baud_base, 16, &uartclk) in uart_set_info() to reject overflowing baud_base values with -EINVAL. Tested in QEMU against Linux 7.3.0-rc3 by calling ioctl(fd, TIOCSSERIAL, &ss) with ss.baud_base = 0x10000001 on /dev/ttyS1: on the unfixed kernel TIOCSSERIAL succeeds (ret = 0) and wraps uport->uartclk to 16 (TIOCGSERIAL reports baud_base = 1), whereas with the fix applied TIOCSSERIAL returns -EINVAL and preserves the existing uport->uartclk. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Fixes: 6eabce6608d6 ("serial: core: check uartclk for zero to avoid divide by zero") Cc: stable@vger.kernel.org Reviewed-by: Ilpo Järvinen Assisted-by: LLM Signed-off-by: Hui Peng --- Changes in v7: - Use check_mul_overflow() instead of raw UINT_MAX / 16 comparison as suggested by Jiri Slaby. drivers/tty/serial/serial_core.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 6ed0195e6912..9a8f4c2e1180 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include #include @@ -931,9 +932,11 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port, old_custom_divisor = uport->custom_divisor; if (!(uport->flags & UPF_FIXED_PORT)) { - unsigned int uartclk = new_info->baud_base * 16; /* check needs to be done here before other settings made */ - if (uartclk == 0) + unsigned int uartclk; + + if (check_mul_overflow(new_info->baud_base, 16, &uartclk) || + uartclk == 0) return -EINVAL; } -- 2.47.3