linux-kernel - Re: [PATCH 07/24] media: dvb-usb-v2: rtl28xxu: fix null-ptr-deref in rtl28xxu_i2c

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Date:   Wed, 17 May 2023 08:55:14 +0200
From:   zzam@...too.org
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Zhang Shurong <zhang_shurong@...mail.com>,
        Antti Palosaari <crope@....fi>, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH 07/24] media: dvb-usb-v2: rtl28xxu: fix null-ptr-deref in
 rtl28xxu_i2c_xfer

Am 13.05.23 um 19:57 schrieb Mauro Carvalho Chehab:
> From: Zhang Shurong <zhang_shurong@...mail.com>
> 
> In rtl28xxu_i2c_xfer, msg is controlled by user. When msg[i].buf
> is null and msg[i].len is zero, former checks on msg[i].buf would be
> passed. Malicious data finally reach rtl28xxu_i2c_xfer. If accessing
> msg[i].buf[0] without sanity check, null ptr deref would happen.
> We add check on msg[i].len to prevent crash.
> 
> Similar commit:
> commit 0ed554fd769a
> ("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")
> 
> Link: https://lore.kernel.org/linux-media/tencent_3623572106754AC2F266B316798B0F6CCA05@qq.com
> Signed-off-by: Zhang Shurong <zhang_shurong@...mail.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@...nel.org>
> ---
>   drivers/media/usb/dvb-usb-v2/rtl28xxu.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/media/usb/dvb-usb-v2/rtl28xxu.c b/drivers/media/usb/dvb-usb-v2/rtl28xxu.c
> index 795a012d4020..f7884bb56fcc 100644
> --- a/drivers/media/usb/dvb-usb-v2/rtl28xxu.c
> +++ b/drivers/media/usb/dvb-usb-v2/rtl28xxu.c
> @@ -176,6 +176,10 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
>   			ret = -EOPNOTSUPP;
>   			goto err_mutex_unlock;
>   		} else if (msg[0].addr == 0x10) {

Is there a need to compare msg[0].addr and msg[1].addr for the combined 
write+read transfer?

@Mauro: It seems a lot of i2c_xfer functions do only partial checking of 
address and direction for these combined write+read transfers. Is this a 
problem?

> +			if (msg[0].len < 1 || msg[1].len < 1) {
> +				ret = -EOPNOTSUPP;
> +				goto err_mutex_unlock;
> +			}
>   			/* method 1 - integrated demod */
>   			if (msg[0].buf[0] == 0x00) {
>   				/* return demod page from driver cache */
> @@ -189,6 +193,10 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
>   				ret = rtl28xxu_ctrl_msg(d, &req);
>   			}
>   		} else if (msg[0].len < 2) {
> +			if (msg[0].len < 1) {
The code sequence is correct, but looks a bit strange. Maybe this is better:
	} else if (msg[0].len < 1) {
		ret = -EOPNOTSUPP;
		goto err_mutex_unlock;
	} else if (msg[0].len < 2) {

> +				ret = -EOPNOTSUPP;
> +				goto err_mutex_unlock;
> +			}
>   			/* method 2 - old I2C */
>   			req.value = (msg[0].buf[0] << 8) | (msg[0].addr << 1);
>   			req.index = CMD_I2C_RD;
> @@ -217,8 +225,16 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
>   			ret = -EOPNOTSUPP;
>   			goto err_mutex_unlock;
>   		} else if (msg[0].addr == 0x10) {
> +			if (msg[0].len < 1) {
Is a write of a single byte fine? req.size below will be 0.

> +				ret = -EOPNOTSUPP;
> +				goto err_mutex_unlock;
> +			}
>   			/* method 1 - integrated demod */
>   			if (msg[0].buf[0] == 0x00) {
> +				if (msg[0].len < 2) {
> +					ret = -EOPNOTSUPP;
> +					goto err_mutex_unlock;
> +				}
>   				/* save demod page for later demod access */
>   				dev->page = msg[0].buf[1];
>   				ret = 0;
> @@ -231,6 +247,10 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
>   				ret = rtl28xxu_ctrl_msg(d, &req);
>   			}
>   		} else if ((msg[0].len < 23) && (!dev->new_i2c_write)) {
> +			if (msg[0].len < 1) {
> +				ret = -EOPNOTSUPP;
> +				goto err_mutex_unlock;
> +			}
>   			/* method 2 - old I2C */
>   			req.value = (msg[0].buf[0] << 8) | (msg[0].addr << 1);
>   			req.index = CMD_I2C_WR;