[PATCH v4 3/5] staging: rtl8723bs: fix out-of-bounds read in portctrl()

[Delene Tchio Romuald]

In portctrl(), when 802.1X port control is enabled and a non-EAPOL
frame is received, the ether_type is read from the LLC header
without verifying that the frame actually contains enough bytes to
hold the MAC header, IV and the LLC header plus two bytes of
ether_type. For sufficiently short frames, the memcpy() that loads
be_tmp reads past the end of the receive buffer.

An attacker within WiFi radio range can exploit this by sending a
crafted short frame. No authentication is required.

Validate the frame length before dereferencing the LLC header; drop
the frame if it is too short.

Found by reviewing length validation in the receive path.
Not tested on hardware.

Fixes: 554c0a3abf216 ("staging: Add rtl8723bs sdio wifi driver")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Luka Gejak <luka.gejak@xxxxxxxxx>
Signed-off-by: Delene Tchio Romuald <delenetchior1@xxxxxxxxx>
---
v4: add Fixes: tag and Cc: stable (Dan Carpenter); carry Luka Gejak's
    Reviewed-by.
v3: rebased on staging-next; sent as numbered series with proper
    Cc from get_maintainer.pl.
v2: rebased on staging-next (v1 was based on v7.0-rc6 and did not
    apply).

 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 00b69571bbb83..c0a1c2ab710ee 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