linux-kernel - [PATCH v2 1/2] staging: rtl8192e: Fix incorrect source in memcpy()

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Message-Id: <20210323113413.29179-1-atulgopinathan@gmail.com>
Date:   Tue, 23 Mar 2021 17:04:12 +0530
From:   Atul Gopinathan <atulgopinathan@...il.com>
To:     gregkh@...uxfoundation.org
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        skhan@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Atul Gopinathan <atulgopinathan@...il.com>,
        stable@...r.kernel.org
Subject: [PATCH v2 1/2] staging: rtl8192e: Fix incorrect source in memcpy()

The variable "info_element" is of the following type:

	struct rtllib_info_element *info_element

defined in drivers/staging/rtl8192e/rtllib.h:

	struct rtllib_info_element {
		u8 id;
		u8 len;
		u8 data[];
	} __packed;

The "len" field defines the size of the "data[]" array. The code is
supposed to check if "info_element->len" is greater than 4 and later
equal to 6. If this is satisfied then, the last two bytes (the 4th and
5th element of u8 "data[]" array) are copied into "network->CcxRmState".

Right now the code uses "memcpy()" with the source as "&info_element[4]"
which would copy in wrong and unintended information. The struct
"rtllib_info_element" has a size of 2 bytes for "id" and "len",
therefore indexing will be done in interval of 2 bytes. So,
"info_element[4]" would point to data which is beyond the memory
allocated for this pointer (that is, at x+8, while "info_element" has
been allocated only from x to x+7 (2 + 6 => 8 bytes)).

This patch rectifies this error by using "&info_element->data[4]" which
correctly copies the last two bytes of "data[]".

NOTE: The faulty line of code came from the following commit:

commit ecdfa44610fa ("Staging: add Realtek 8192 PCI wireless driver")

The above commit created the file `rtl8192e/ieee80211/ieee80211_rx.c`
which had the faulty line of code. This file has been deleted (or
possibly renamed) with the contents copied in to a new file
`rtl8192e/rtllib_rx.c` along with additional code in the commit
94a799425eee (tagged in Fixes).

Fixes: 94a799425eee ("[PATCH 1/8] rtl8192e: Import new version of driver from realtek")
Cc: stable@...r.kernel.org
Signed-off-by: Atul Gopinathan <atulgopinathan@...il.com>
---
 drivers/staging/rtl8192e/rtllib_rx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8192e/rtllib_rx.c b/drivers/staging/rtl8192e/rtllib_rx.c
index 8415f26fd4c0..6e48b31a9afc 100644
--- a/drivers/staging/rtl8192e/rtllib_rx.c
+++ b/drivers/staging/rtl8192e/rtllib_rx.c
@@ -1965,15 +1965,15 @@ static void rtllib_parse_mife_generic(struct rtllib_device *ieee,

 	if (info_element->len > 4 &&
 	    info_element->data[0] == 0x00 &&
 	    info_element->data[1] == 0x40 &&
 	    info_element->data[2] == 0x96 &&
 	    info_element->data[3] == 0x01) {
 		if (info_element->len == 6) {
-			memcpy(network->CcxRmState, &info_element[4], 2);
+			memcpy(network->CcxRmState, &info_element->data[4], 2);
 			if (network->CcxRmState[0] != 0)
 				network->bCcxRmEnable = true;
 			else
 				network->bCcxRmEnable = false;
 			network->MBssidMask = network->CcxRmState[1] & 0x07;
 			if (network->MBssidMask != 0) {
 				network->bMBssidValid = true;
-- 
2.25.1