[PATCH] staging: rtl8723bs: fix frame length underflow in OnAuthClient

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

If pkt_len is less than WLAN_HDR_A3_LEN + offset + 6, the reads of
the seq and status fields go beyond the frame buffer. Additionally,
when pkt_len < WLAN_HDR_A3_LEN + _AUTH_IE_OFFSET_ (30 bytes), the
subtraction passed to rtw_get_ie() wraps around since pkt_len is
unsigned, causing rtw_get_ie() to scan well past the end of the buffer.

Add a minimum length check after computing offset to reject frames
that are too short before any fixed field access.

Reported-by: Dan Carpenter <error27@gmail.com>
Fixes: 554c0a3abf21 ("staging: Add rtl8723bs sdio wifi driver")
Cc: stable@vger.kernel.org
Signed-off-by: Alexandru Hossu <hossu.alexandru@gmail.com>
---
 drivers/staging/rtl8723bs/core/rtw_mlme_ext.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c b/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c
index 90f27665667a..6b0ac54ad3d4 100644
--- a/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c
+++ b/drivers/staging/rtl8723bs/core/rtw_mlme_ext.c
@@ -869,6 +869,9 @@ unsigned int OnAuthClient(struct adapter *padapter, union recv_frame *precv_fram
 
 	offset = (GetPrivacy(pframe)) ? 4 : 0;
 
+	if (pkt_len < WLAN_HDR_A3_LEN + offset + 6)
+		goto authclnt_fail;
+
 	seq	= le16_to_cpu(*(__le16 *)((SIZE_PTR)pframe + WLAN_HDR_A3_LEN + offset + 2));
 	status	= le16_to_cpu(*(__le16 *)((SIZE_PTR)pframe + WLAN_HDR_A3_LEN + offset + 4));
 
-- 
2.53.0