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

From: Manivannan Sadhasivam
Date: Sat May 09 2020 - 01:49:22 EST


On Fri, May 08, 2020 at 07:26:44PM -0700, Bhaumik Bhatt wrote:
> From: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> Reviewed-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>

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

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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