[PATCH 2/5] staging: rtl8723bs: fix OOB read / stack overflow in rtw_get_wps_attr()

[Muhammad Bilal <meatuni001@gmail.com>]

rtw_get_wps_attr() walks WPS attributes inside a WPS IE taken from
a wireless management frame. For each candidate attribute it only
checks that the fixed 4-byte attribute header (2-byte ID + 2-byte
length) fits inside the IE:

	if (attr_ptr + 4 > wps_ie + wps_ielen)
		break;
	u16 attr_id = get_unaligned_be16(attr_ptr);
	u16 attr_data_len = get_unaligned_be16(attr_ptr + 2);
	u16 attr_len = attr_data_len + 4;

attr_data_len (and therefore attr_len) is read directly from the
wire and is never checked against the remaining bytes in the IE
before being used as the size of:

	memcpy(buf_attr, attr_ptr, attr_len);

Since attr_len is fully attacker controlled (0 to 65535+4), this is
both a heap OOB read of wps_ie, and, more seriously, a stack buffer
overflow at several call sites where buf_attr is a single-byte
stack variable, e.g. rtw_get_wps_attr_content()'s callers passing
WPS_ATTR_SELECTED_REGISTRAR into a stack "u8 sr"/"u8
selected_registrar" (drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c,
drivers/staging/rtl8723bs/core/rtw_mlme_ext.c). A crafted WPS IE in a
beacon or probe response processed during scanning can therefore
smash the stack of the parsing thread.

rtw_get_wps_attr_content() itself has no independent length check
and simply trusts the attr_len it gets back from rtw_get_wps_attr(),
so fixing the bound here also fixes that caller.

The "attr_ptr + 4 > wps_ie + wps_ielen" header check above was added
by commit 1463ca3ec6601 ("staging: rtl8723bs: fix OOB reads in
rtw_get_sec_ie(), rtw_get_wapi_ie(), and rtw_get_wps_attr()"), which
bounded the fixed header but never extended the check to cover the
variable-length attribute data that follows it. Add that missing
check before attr_len is used as a memcpy() length or accepted as a
match.

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 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/staging/rtl8723bs/core/rtw_ieee80211.c b/drivers/staging/rtl8723bs/core/rtw_ieee80211.c
index 2fb5863dbeef..be374d222c55 100644
--- a/drivers/staging/rtl8723bs/core/rtw_ieee80211.c
+++ b/drivers/staging/rtl8723bs/core/rtw_ieee80211.c
@@ -733,6 +733,10 @@ u8 *rtw_get_wps_attr(u8 *wps_ie, uint wps_ielen, u16 target_attr_id, u8 *buf_att
 		u16 attr_data_len = get_unaligned_be16(attr_ptr + 2);
 		u16 attr_len = attr_data_len + 4;
 
+		/* Reject attributes whose claimed length runs past the IE */
+		if (attr_ptr + attr_len > wps_ie + wps_ielen)
+			break;
+
 		if (attr_id == target_attr_id) {
 			target_attr_ptr = attr_ptr;
 
-- 
2.55.0