[v3,4/9] bus: mhi: core: Read transfer length from an event properly

Commit Message

Bhaumik Bhatt April 29, 2020, 8:52 p.m. UTC

From: Hemant Kumar <[e-mail]>

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 <[e-mail]>
Signed-off-by: Bhaumik Bhatt <[e-mail]>
---
 drivers/bus/mhi/core/main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Jeffrey Hugo April 30, 2020, 2:28 p.m. UTC | #1

On 4/29/2020 2:52 PM, Bhaumik Bhatt wrote:
> From: Hemant Kumar <[e-mail]>
> 
> 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 <[e-mail]>
> Signed-off-by: Bhaumik Bhatt <[e-mail]>
> ---

Reviewed-by: Jeffrey Hugo <[e-mail]>

Patch

diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
index b8e4aac..0afbaa1 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;