[PATCH 2/5] accel/qaic: tighten bounds checking in decode_message()

[Pranjal Ramajor Asha Kanojiya]

On 6/21/2023 12:51 PM, Dan Carpenter wrote:
> Copy the bounds checking from encode_message() to decode_message().
> 
> This patch addresses the following concerns.  Ensure that there is
> enough space for at least one header so that we don't have a negative
> size later.
> 
> 	if (msg_hdr_len < sizeof(*trans_hdr))
> 
> Ensure that we have enough space to read the next header from the
> msg->data.
> 
> 	if (msg_len >= msg_hdr_len - sizeof(*trans_hdr))
> 		return -EINVAL;
> 
> Check that the trans_hdr->len is not below the minimum size:
> 
> 	if (hdr_len < sizeof(*trans_hdr))
> 
> This minimum check ensures that we don't corrupt memory in
> decode_passthrough() when we do.
> 
> 	memcpy(out_trans->data, in_trans->data, len - sizeof(in_trans->hdr));
> 
> And finally, use size_add() to prevent an integer overflow:
> 
> 	if (size_add(msg_len, hdr_len) > msg_hdr_len)
> 
> Fixes: 129776ac2e38 ("accel/qaic: Add control path")
> Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
> ---
>   drivers/accel/qaic/qaic_control.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/accel/qaic/qaic_control.c b/drivers/accel/qaic/qaic_control.c
> index a51b1594dcfa..78f6c3d6380d 100644
> --- a/drivers/accel/qaic/qaic_control.c
> +++ b/drivers/accel/qaic/qaic_control.c
> @@ -955,15 +955,23 @@ static int decode_message(struct qaic_device *qdev, struct manage_msg *user_msg,
>   	int ret;
>   	int i;
>   
> -	if (msg_hdr_len > QAIC_MANAGE_MAX_MSG_LENGTH)
> +	if (msg_hdr_len < sizeof(*trans_hdr) ||
> +	    msg_hdr_len > QAIC_MANAGE_MAX_MSG_LENGTH)
>   		return -EINVAL;
>   
>   	user_msg->len = 0;
>   	user_msg->count = le32_to_cpu(msg->hdr.count);
>   
>   	for (i = 0; i < user_msg->count; ++i) {
> +		u32 hdr_len;
> +
> +		if (msg_len >= msg_hdr_len - sizeof(*trans_hdr))
> +			return -EINVAL;
If I understand correctly this check is added to verify if we are left 
with trans_hdr size of data. In that case '>' comparison operator should 
be used.
> +
>   		trans_hdr = (struct wire_trans_hdr *)(msg->data + msg_len);
> -		if (msg_len + le32_to_cpu(trans_hdr->len) > msg_hdr_len)
> +		hdr_len = le32_to_cpu(trans_hdr->len);
> +		if (hdr_len < sizeof(*trans_hdr) ||
> +		    size_add(msg_len, hdr_len) > msg_hdr_len)
>   			return -EINVAL;
>   
>   		switch (le32_to_cpu(trans_hdr->type)) {