[PATCH AUTOSEL 5.7 256/388] bus: mhi: core: Read transfer length from an event properly

[Sasha Levin]

From: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>

[ Upstream commit ee75cedf82d832561af8ba8380aeffd00a9eea77 ]

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>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200521170249.21795-5-manivannan.sadhasivam@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 97e06cc586e4..8be3d0fb0614 100644
--- a/drivers/bus/mhi/core/main.c
+++ b/drivers/bus/mhi/core/main.c
@@ -513,7 +513,10 @@ 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;
@@ -597,7 +600,9 @@ 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;
 
-- 
2.25.1