Re: [PATCH V2] media: dvb-usb: Optimizing err() output

[Hans Verkuil <hverkuil+cisco@kernel.org>]

On 14/10/2025 02:30, Edward Adam Davis wrote:
> syzbot reported a uninit-value in pctv452e_i2c_msg. [1]
> 
> When the snd_len or rcv_len check fails and jumps to failed, buf is
> uninitialized, triggering the uninit-value issue.
> 
> Setting the err() output buf byte count to 0 before jumping to failed
> before initializing buf and setting it to 7 after initializing buf avoids
> this warning.
> 
> [1]
> BUG: KMSAN: uninit-value in hex_string+0x681/0x740 lib/vsprintf.c:1220
>  pctv452e_i2c_msg+0x82a/0x8f0 drivers/media/usb/dvb-usb/pctv452e.c:467
>  pctv452e_i2c_xfer+0x2e6/0x4c0 drivers/media/usb/dvb-usb/pctv452e.c:502
> 
> Reported-by: syzbot+480edd2cadb85ddb4bbe@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> V1 -> V2: subject typos
> 
>  drivers/media/usb/dvb-usb/pctv452e.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/usb/dvb-usb/pctv452e.c b/drivers/media/usb/dvb-usb/pctv452e.c
> index 5094de9a312e..3b6e86a8e9ff 100644
> --- a/drivers/media/usb/dvb-usb/pctv452e.c
> +++ b/drivers/media/usb/dvb-usb/pctv452e.c
> @@ -420,7 +420,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
>  	struct pctv452e_state *state = d->priv;
>  	u8 *buf;
>  	u8 id;
> -	int ret;
> +	int ret, plen = 0;

Adding a plen variable isn't the right fix...

>  
>  	buf = kmalloc(64, GFP_KERNEL);
>  	if (!buf)
> @@ -432,6 +432,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
>  	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
>  		goto failed;

...this check should be moved up to before the kmalloc and just return -EINVAL.
That also avoids incrementing state->c in that case.

Regards,

	Hans

>  
> +	plen = 7;
>  	buf[0] = SYNC_BYTE_OUT;
>  	buf[1] = id;
>  	buf[2] = PCTV_CMD_I2C;
> @@ -466,7 +467,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
>  failed:
>  	err("I2C error %d; %02X %02X  %02X %02X %02X -> %*ph",
>  	     ret, SYNC_BYTE_OUT, id, addr << 1, snd_len, rcv_len,
> -	     7, buf);
> +	     plen, buf);
>  
>  	kfree(buf);
>  	return ret;