[PATCH v6 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; 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@vger.kernel.org
Signed-off-by: Delene Tchio Romuald <delenetchior1@gmail.com>
---
v6: drop the unrelated cleanups (ptr = ptr + X -> ptr += X,
    ether_type inversion into direct return NULL); the patch
    now only adds the short-frame length check before
    dereferencing the LLC header (Dan Carpenter).
v5: return NULL directly on the short-frame and non-EAPOL
    error paths (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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index e30617875a69d..b476f7a03a234 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -539,6 +539,14 @@ static union recv_frame *portctrl(struct adapter *adapter, union recv_frame *pre
 
 			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;
 			memcpy(&be_tmp, ptr, 2);
-- 
2.43.0