[PATCH v5 3/5] staging: rtl8723bs: fix out-of-bounds read in portctrl()

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

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 and
return early on short frames and on non-EAPOL frames, rather than
staging the result in prtnframe.

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

Fixes: 554c0a3abf216 ("staging: Add rtl8723bs sdio wifi driver")
Cc: stable@vger.kernel.org
Signed-off-by: Delene Tchio Romuald <delenetchior1@gmail.com>
---
v5: return NULL directly on the short-frame and non-EAPOL
    error paths instead of staging the result through
    prtnframe (Dan Carpenter).
v4: add Fixes: tag and Cc: stable (Dan Carpenter).
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 | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index 40884788a30d6..b11982fbe7e1f 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -537,20 +537,25 @@ static union recv_frame *portctrl(struct adapter *adapter, union recv_frame *pre
 			/* blocked */
 			/* only accept EAPOL frame */
 
-			prtnframe = precv_frame;
+			/* 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);
+				return NULL;
+			}
 
 			/* get ether_type */
-			ptr = ptr + pfhdr->attrib.hdrlen + pfhdr->attrib.iv_len + LLC_HEADER_LENGTH;
+			ptr += pattrib->hdrlen + pattrib->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);
-				prtnframe = NULL;
+			if (ether_type != eapol_type) {
+				rtw_free_recvframe(precv_frame,
+						   &adapter->recvpriv.free_recv_queue);
+				return NULL;
 			}
+			prtnframe = precv_frame;
 		} else {
 			/* allowed */
 			/* check decryption status, and decrypt the frame if needed */
-- 
2.43.0