[PATCH] staging: rtl8723bs: fix protected RX frame validation in decrypt path

[Tianchu Chen]

From: Tianchu Chen <flynnnchen@xxxxxxxxxxx>

The RX software decrypt path mishandles crafted protected frames from a
malicious AP in two ways:

1) decryptor() never checks that a protected frame is long enough to
hold the 802.11 header plus the per-cipher trailer(IV, ICV/MIC).

Implementations like rtw_wep_decrypt() and rtw_aes_decrypt() all compute
length = hdr.len - hdrlen - iv_len. and a shorter frame underflows the 
unsigned subtraction, turning into OOB reads/writes.

Reject such frames in decryptor() before touching the IV.

2) validate_80211w_mgmt() uses the skb before checking whether
decryptor() returned NULL. On decrypt failure the skb has been freed
before being used.

Bail out immediately when decryptor() fails.

Discovered by Atuin - Automated Vulnerability Discovery Engine.

Fixes: 554c0a3abf21 ("staging: Add rtl8723bs sdio wifi driver")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Tianchu Chen <flynnnchen@xxxxxxxxxxx>
---
 drivers/staging/rtl8723bs/core/rtw_recv.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index 7568fc514d7ce..4756e0fedd46f 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -426,8 +426,21 @@ static union recv_frame *decryptor(struct adapter *padapter, union recv_frame *p
 	u32  res = _SUCCESS;
 
 	if (prxattrib->encrypt > 0) {
-		u8 *iv = precv_frame->u.hdr.rx_data + prxattrib->hdrlen;
+		u8 *iv;
+		u32 min_len = prxattrib->hdrlen + prxattrib->iv_len + prxattrib->icv_len;
 
+		/* TKIP appends an 8-byte Michael MIC that icv_len doesn't account for */
+		if (prxattrib->encrypt == _TKIP_)
+			min_len += 8;
+
+		/* a protected frame must be long enough to hold the IV and ICV/MIC */
+		if (precv_frame->u.hdr.len < min_len) {
+			rtw_free_recvframe(precv_frame,
+					   &padapter->recvpriv.free_recv_queue);
+			return NULL;
+		}
+
+		iv = precv_frame->u.hdr.rx_data + prxattrib->hdrlen;
 		prxattrib->key_index = (((iv[3]) >> 6) & 0x3);
 
 		if (prxattrib->key_index > WEP_KEYS) {
@@ -1395,6 +1408,10 @@ static signed int validate_80211w_mgmt(struct adapter *adapter, union recv_frame
 			if (!mgmt_DATA)
 				goto validate_80211w_fail;
 			precv_frame = decryptor(adapter, precv_frame);
+			if (!precv_frame) {
+				kfree(mgmt_DATA);
+				goto validate_80211w_fail;
+			}
 			/* save actual management data frame body */
 			memcpy(mgmt_DATA, ptr + pattrib->hdrlen + pattrib->iv_len, data_len);
 			/* overwrite the iv field */
@@ -1402,8 +1419,6 @@ static signed int validate_80211w_mgmt(struct adapter *adapter, union recv_frame
 			/* remove the iv and icv length */
 			pattrib->pkt_len = pattrib->pkt_len - pattrib->iv_len - pattrib->icv_len;
 			kfree(mgmt_DATA);
-			if (!precv_frame)
-				goto validate_80211w_fail;
 		} else if (is_multicast_ether_addr(GetAddr1Ptr(ptr)) &&
 			(subtype == WIFI_DEAUTH || subtype == WIFI_DISASSOC)) {
 			signed int BIP_ret = _SUCCESS;
-- 
2.51.0