[PATCH 126/379][SRU][OEM-5.6] bus: mhi: core: Read transfer length from an event properly

[You-Sheng Yang]

From: Hemant Kumar <hemantk at codeaurora.org>

BugLink: https://bugs.launchpad.net/bugs/1879633

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 at codeaurora.org>
Signed-off-by: Bhaumik Bhatt <bbhatt at codeaurora.org>
Reviewed-by: Jeffrey Hugo <jhugo at codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
Link: https://lore.kernel.org/r/20200521170249.21795-5-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit ee75cedf82d832561af8ba8380aeffd00a9eea77)
Signed-off-by: You-Sheng Yang <vicamo.yang at canonical.com>
---
 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 30798ec3950a..6a8066640e78 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;
 
-- 
2.29.2