linux-kernel - Re: [PATCH 5/5] staging: r8188eu: turbo scan is always off for r8188eu

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Message-ID: <YdSzNFZ+DXX6gemR@martin-debian-1.paytec.ch>
Date:   Tue, 4 Jan 2022 21:51:00 +0100
From:   Martin Kaiser <martin@...ser.cx>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Michael Straube <straube.linux@...il.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] staging: r8188eu: turbo scan is always off for
 r8188eu

Hi Pavel,

Thus wrote Pavel Skripkin (paskripkin@...il.com):

> It's a bit unrelated to the patch, but I found it while reviewing this. It's
> in the same function rtl8188e_PHY_RF6052SetCckTxPower():

> 89: 	u32 TxAGC[2] = {0, 0};
> ...
> 92	u8 *ptr;
> ...
> 129	for (idx1 = RF_PATH_A; idx1 <= RF_PATH_B; idx1++) {
> 130		ptr = (u8 *)(&TxAGC[idx1]);
> 131		for (idx2 = 0; idx2 < 4; idx2++) {
> 132			if (*ptr > RF6052_MAX_TX_PWR)
> 133				*ptr = RF6052_MAX_TX_PWR;
> 134			ptr++;
> 135		}
> 136	}


> What is going on here? Code just checks and writes to random place on stack
> outside TxAGC array? I might be missing something, but it looks wrong...

TxAGC is two 32-bit values, i.e. 2 x 4 Bytes. The outer loop selects a
32-bit array entry, the inner loop iterates over each byte of this entry
and checks that it is <= RF6052_MAX_TX_PWR. I don't think this writes past
the end of the TxAGC[] array.

The rtlwifi driver contains a similar check in
rtl92ce_phy_rf6052_set_cck_txpower().

Best regards,
Martin