linux-kernel - Re: [PATCH 05/24] media: dvb-usb-v2: ec168: fix null-ptr-deref in ec168_i2c

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Date:   Wed, 17 May 2023 07:10:34 +0200
From:   zzam@...too.org
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Wei Chen <harperchen1110@...il.com>,
        Antti Palosaari <crope@....fi>, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH 05/24] media: dvb-usb-v2: ec168: fix null-ptr-deref in
 ec168_i2c_xfer()

Am 13.05.23 um 19:57 schrieb Mauro Carvalho Chehab:
> From: Wei Chen <harperchen1110@...il.com>
> 
> In ec168_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.
> If accessing msg[i].buf[0] without sanity check, null pointer 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()")
> 
Review comment below.

> Link: https://lore.kernel.org/linux-media/20230313085853.3252349-1-harperchen1110@gmail.com
> Signed-off-by: Wei Chen <harperchen1110@...il.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@...nel.org>
> ---
>   drivers/media/usb/dvb-usb-v2/ec168.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/media/usb/dvb-usb-v2/ec168.c b/drivers/media/usb/dvb-usb-v2/ec168.c
> index 7ed0ab9e429b..0e4773fc025c 100644
> --- a/drivers/media/usb/dvb-usb-v2/ec168.c
> +++ b/drivers/media/usb/dvb-usb-v2/ec168.c
> @@ -115,6 +115,10 @@ static int ec168_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
>   	while (i < num) {
>   		if (num > i + 1 && (msg[i+1].flags & I2C_M_RD)) {
>   			if (msg[i].addr == ec168_ec100_config.demod_address) {
> +				if (msg[i].len < 1) {
> +					i = -EOPNOTSUPP;
> +					break;
> +				}
>   				req.cmd = READ_DEMOD;
>   				req.value = 0;
>   				req.index = 0xff00 + msg[i].buf[0]; /* reg */
> @@ -131,6 +135,10 @@ static int ec168_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
>   			}
>   		} else {
>   			if (msg[i].addr == ec168_ec100_config.demod_address) {
> +				if (msg[i].len < 1) {
> +					i = -EOPNOTSUPP;
> +					break;
> +				}
The check condition should be msg[i].len < 2 or != 2. The following 
lines access msg[i].buf elements 0 and 1.
>   				req.cmd = WRITE_DEMOD;
>   				req.value = msg[i].buf[1]; /* val */
>   				req.index = 0xff00 + msg[i].buf[0]; /* reg */
> @@ -139,6 +147,10 @@ static int ec168_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
>   				ret = ec168_ctrl_msg(d, &req);
>   				i += 1;
>   			} else {
> +				if (msg[i].len < 1) {
> +					i = -EOPNOTSUPP;
> +					break;
> +				}
>   				req.cmd = WRITE_I2C;
>   				req.value = msg[i].buf[0]; /* val */
>   				req.index = 0x0100 + msg[i].addr; /* I2C addr */