[PATCH v3 3/5] staging: rtl8723bs: fix out-of-bounds read in portctrl()

[Delene Tchio Romuald <delenetchior1@gmail.com>]

In portctrl(), the pointer is advanced by hdrlen + iv_len +
LLC_HEADER_LENGTH and then 2 bytes are read via memcpy() to extract
the ether_type field. There is no check that the frame is large
enough to contain these fields, so a short frame leads to an
out-of-bounds read on kernel heap memory.

This code is reachable during 802.1X authentication when the station
is in the ieee8021x_blocked state.

Add a frame length check before the pointer arithmetic and wrap the
existing ether_type extraction in the else branch so that short
frames are dropped safely.

Found by reviewing memory operations in the driver.
Not tested on hardware.

Signed-off-by: Delene Tchio Romuald <delenetchior1@gmail.com>
---
v3:
 - Rebased on staging-next
 - Sent as numbered series with proper Cc from get_maintainer.pl
v2:
 - Rebased on staging-next

 drivers/staging/rtl8723bs/core/rtw_recv.c | 28 +++++++++++++++--------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index 11ae99e53b86a..8e38cb9791755 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -539,17 +539,25 @@ static union recv_frame *portctrl(struct adapter *adapter, union recv_frame *pre
 
 			prtnframe = precv_frame;
 
-			/* get ether_type */
-			ptr = ptr + pfhdr->attrib.hdrlen + pfhdr->attrib.iv_len + LLC_HEADER_LENGTH;
-			memcpy(&be_tmp, ptr, 2);
-			ether_type = ntohs(be_tmp);
-
-			if (ether_type == eapol_type)
-				prtnframe = precv_frame;
-			else {
-				/* free this frame */
-				rtw_free_recvframe(precv_frame, &adapter->recvpriv.free_recv_queue);
+			/* Ensure frame has LLC header and ether_type */
+			if (pfhdr->len < pattrib->hdrlen +
+			    pattrib->iv_len + LLC_HEADER_LENGTH + 2) {
+				rtw_free_recvframe(precv_frame,
+						   &adapter->recvpriv.free_recv_queue);
 				prtnframe = NULL;
+			} else {
+				/* get ether_type */
+				ptr += pattrib->hdrlen +
+				       pattrib->iv_len +
+				       LLC_HEADER_LENGTH;
+				memcpy(&be_tmp, ptr, 2);
+				ether_type = ntohs(be_tmp);
+
+				if (ether_type != eapol_type) {
+					rtw_free_recvframe(precv_frame,
+							   &adapter->recvpriv.free_recv_queue);
+					prtnframe = NULL;
+				}
 			}
 		} else {
 			/* allowed */
-- 
2.43.0