Re: [PATCH v4] serial: core: reject baud_base values that overflow port->uartclk in uart_set_info()

[sashiko-bot@kernel.org]

> 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).
> 
> Reject new_info->baud_base > UINT_MAX / 16 before multiplying by 16 in
> uart_set_info().
> 
> 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
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260924060511.2364717-4-benquike@gmail.com?part=1