[PATCH 3/5] staging: rtl8723bs: fix OOB read in rtw_action_frame_parse()

[Muhammad Bilal <meatuni001@gmail.com>]

rtw_action_frame_parse() takes a frame_len parameter but never
actually checks it before indexing into the frame body:

	const u8 *frame_body = frame + sizeof(struct ieee80211_hdr_3addr);
	...
	c = frame_body[0];
	...
	a = frame_body[1];

frame_body already points 24 bytes (sizeof(struct
ieee80211_hdr_3addr)) into frame, so reading frame_body[0] and
frame_body[1] requires frame_len >= 26. A management action frame
shorter than that (e.g. exactly 24 bytes, the minimum a malicious
peer can send) causes a 1-2 byte out-of-bounds read.

This is reachable from rtw_cfg80211_monitor_if_xmit_entry() and
cfg80211_rtw_mgmt_tx() in ioctl_cfg80211.c, both of which pass
attacker/user-influenced frame buffers and lengths straight through.

Add the missing length check before frame_body is dereferenced.

Fixes: 554c0a3abf216 ("staging: Add rtl8723bs sdio wifi driver")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
 drivers/staging/rtl8723bs/core/rtw_ieee80211.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/staging/rtl8723bs/core/rtw_ieee80211.c b/drivers/staging/rtl8723bs/core/rtw_ieee80211.c
index be374d222c55..e02b54131633 100644
--- a/drivers/staging/rtl8723bs/core/rtw_ieee80211.c
+++ b/drivers/staging/rtl8723bs/core/rtw_ieee80211.c
@@ -1145,6 +1145,9 @@ int rtw_action_frame_parse(const u8 *frame, u32 frame_len, u8 *category, u8 *act
 	u8 c;
 	u8 a = ACT_PUBLIC_MAX;
 
+	if (frame_len < sizeof(struct ieee80211_hdr_3addr) + 2)
+		return false;
+
 	fc = le16_to_cpu(((struct ieee80211_hdr_3addr *)frame)->frame_control);
 
 	if ((fc & (IEEE80211_FCTL_FTYPE | IEEE80211_FCTL_STYPE)) !=
-- 
2.55.0