Re: [PATCH v7 4/8] bus: mhi: core: Read transfer length from an event properly

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Fri, May 08, 2020 at 07:26:44PM -0700, Bhaumik Bhatt wrote:
> From: Hemant Kumar <hemantk@codeaurora.org>
> 
> When MHI Driver receives an EOT event, it reads xfer_len from the
> event in the last TRE. The value is under control of the MHI device
> and never validated by Host MHI driver. The value should never be
> larger than the real size of the buffer but a malicious device can
> set the value 0xFFFF as maximum. This causes driver to memory
> overflow (both read or write). Fix this issue by reading minimum of
> transfer length from event and the buffer length provided.
> 
> Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
> Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Thanks,
Mani

> ---
>  drivers/bus/mhi/core/main.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 30798ec..6a80666 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -514,7 +514,10 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
>  				mhi_cntrl->unmap_single(mhi_cntrl, buf_info);
>  
>  			result.buf_addr = buf_info->cb_buf;
> -			result.bytes_xferd = xfer_len;
> +
> +			/* truncate to buf len if xfer_len is larger */
> +			result.bytes_xferd =
> +				min_t(u16, xfer_len, buf_info->len);
>  			mhi_del_ring_element(mhi_cntrl, buf_ring);
>  			mhi_del_ring_element(mhi_cntrl, tre_ring);
>  			local_rp = tre_ring->rp;
> @@ -598,7 +601,9 @@ static int parse_rsc_event(struct mhi_controller *mhi_cntrl,
>  
>  	result.transaction_status = (ev_code == MHI_EV_CC_OVERFLOW) ?
>  		-EOVERFLOW : 0;
> -	result.bytes_xferd = xfer_len;
> +
> +	/* truncate to buf len if xfer_len is larger */
> +	result.bytes_xferd = min_t(u16, xfer_len, buf_info->len);
>  	result.buf_addr = buf_info->cb_buf;
>  	result.dir = mhi_chan->dir;
>  
> -- 
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