linux-kernel - Re: [PATCH 04/24] media: dvb-usb: az6027: fix three null-ptr-deref in az6027_i2c

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Date:   Wed, 17 May 2023 07:06:09 +0200
From:   zzam@...too.org
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Wei Chen <harperchen1110@...il.com>, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH 04/24] media: dvb-usb: az6027: fix three null-ptr-deref in
 az6027_i2c_xfer()

Am 13.05.23 um 19:57 schrieb Mauro Carvalho Chehab:
> From: Wei Chen <harperchen1110@...il.com>
> 
> In az6027_i2c_xfer, msg is controlled by user. When msg[i].buf is null,
> commit 0ed554fd769a ("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")
> fix the null-ptr-deref bug when msg[i].addr is 0x99. However, null-ptr-deref
> also happens when msg[i].addr is 0xd0 and 0xc0. We add check on msg[i].len to
> prevent null-ptr-deref.
> 
Some added checks still allow too short buffers.
> Link: https://lore.kernel.org/linux-media/20230310165604.3093483-1-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/az6027.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/media/usb/dvb-usb/az6027.c b/drivers/media/usb/dvb-usb/az6027.c
> index 7d78ee09be5e..a31c6f82f4e9 100644
> --- a/drivers/media/usb/dvb-usb/az6027.c
> +++ b/drivers/media/usb/dvb-usb/az6027.c
> @@ -988,6 +988,10 @@ static int az6027_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[], int n
>   			/* write/read request */
>   			if (i + 1 < num && (msg[i + 1].flags & I2C_M_RD)) {
>   				req = 0xB9;
> +				if (msg[i].len < 1) {
> +					i = -EOPNOTSUPP;
> +					break;
> +				}

The following line accesses the elements 0 and 1. Shouldn't this code 
check for msg[i].len < 2.
Or even msg[i].len != 2? Too long input seems just to get ignored.

>   				index = (((msg[i].buf[0] << 8) & 0xff00) | (msg[i].buf[1] & 0x00ff));
>   				value = msg[i].addr + (msg[i].len << 8);
>   				length = msg[i + 1].len + 6;
> @@ -1001,6 +1005,10 @@ static int az6027_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[], int n
>   
>   				/* demod 16bit addr */
>   				req = 0xBD;
> +				if (msg[i].len < 1) {
> +					i = -EOPNOTSUPP;
> +					break;
> +				}
Same here, at least two elements are used.

>   				index = (((msg[i].buf[0] << 8) & 0xff00) | (msg[i].buf[1] & 0x00ff));
>   				value = msg[i].addr + (2 << 8);
>   				length = msg[i].len - 2;
> @@ -1026,6 +1034,10 @@ static int az6027_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[], int n
>   			} else {
>   
>   				req = 0xBD;
> +				if (msg[i].len < 1) {
> +					i = -EOPNOTSUPP;
> +					break;
> +				}
>   				index = msg[i].buf[0] & 0x00FF;
>   				value = msg[i].addr + (1 << 8);
>   				length = msg[i].len - 1;