Re: [PATCH v2 3/8] bus: mhi: core: Read transfer length from an event properly

[Jeffrey Hugo <jhugo@codeaurora.org>]

On 4/27/2020 8:59 PM, 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 device to memory

The device will overflow, or the driver?

> 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>
> ---
>   drivers/bus/mhi/core/main.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 1ccd4cc..3d468d9 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -521,7 +521,10 @@ 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;
> 


-- 
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.