[PATCH v9] staging: rtl8723bs: fix WEP length underflow and OOB read in OnAuth()

[Alexandru Hossu <hossu.alexandru@gmail.com>]

OnAuth() has two bugs in the shared-key authentication path.

When the Privacy bit is set, rtw_wep_decrypt() is called without
verifying that the frame is long enough to contain a valid WEP IV and
ICV.  Inside rtw_wep_decrypt(), length is computed as:

    length = len - WLAN_HDR_A3_LEN - iv_len

and then passed as (length - 4) to crc32_le().  If len is less than
WLAN_HDR_A3_LEN + iv_len + icv_len (32 bytes), length - 4 is negative
and, after the implicit cast to size_t, causes crc32_le() to read far
beyond the frame buffer.  Add a minimum length check before accessing
the IV field and calling the decryption path.

When processing a seq=3 response, rtw_get_ie() stores the Challenge
Text IE length in ie_len, but the subsequent memcmp() always reads 128
bytes regardless of ie_len.  IEEE 802.11 mandates a challenge text of
exactly 128 bytes; reject any IE whose length field differs, matching
the check already applied to OnAuthClient().

Fixes: 554c0a3abf21 ("staging: Add rtl8723bs sdio wifi driver")
Cc: stable@vger.kernel.org
Signed-off-by: Alexandru Hossu <hossu.alexandru@gmail.com>
---
v9: add WLAN_HDR_A3_LEN guard and WEP minimum length check before
    iv[3] access and rtw_wep_decrypt(); tighten ie_len check from
    <= 0 to != 128 to reject under-size challenge IEs

 drivers/staging/rtl8723bs/core/rtw_mlme_ext.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c b/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c
index 68ce422305ed..8575b7bd6d84 100644
--- a/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c
+++ b/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c
@@ -687,6 +687,9 @@ unsigned int OnAuth(struct adapter *padapter, union recv_frame *precv_frame)
 	if ((pmlmeinfo->state&0x03) != WIFI_FW_AP_STATE)
 		return _FAIL;
 
+	if (len < WLAN_HDR_A3_LEN)
+		return _FAIL;
+
 	sa = GetAddr2Ptr(pframe);
 
 	auth_mode = psecuritypriv->dot11AuthAlgrthm;
@@ -698,6 +701,9 @@ unsigned int OnAuth(struct adapter *padapter, union recv_frame *precv_frame)
 		prxattrib->hdrlen = WLAN_HDR_A3_LEN;
 		prxattrib->encrypt = _WEP40_;
 
+		if (len < WLAN_HDR_A3_LEN + 8)
+			return _FAIL;
+
 		iv = pframe+prxattrib->hdrlen;
 		prxattrib->key_index = ((iv[3]>>6)&0x3);
 
@@ -802,7 +808,7 @@ unsigned int OnAuth(struct adapter *padapter, union recv_frame *precv_frame)
 			p = rtw_get_ie(pframe + WLAN_HDR_A3_LEN + 4 + _AUTH_IE_OFFSET_, WLAN_EID_CHALLENGE, (int *)&ie_len,
 					len - WLAN_HDR_A3_LEN - _AUTH_IE_OFFSET_ - 4);
 
-			if (!p || ie_len <= 0) {
+			if (!p || ie_len != 128) {
 				status = WLAN_STATUS_CHALLENGE_FAIL;
 				goto auth_fail;
 			}
-- 
2.54.0