linux-kernel - Re: [mt76/mt7603/mac] Question about missing variable assignment

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Date:   Sun, 3 Mar 2019 11:05:51 +0100
From:   Felix Fietkau <nbd@....name>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Lorenzo Bianconi <lorenzo.bianconi83@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [mt76/mt7603/mac] Question about missing variable assignment

On 2019-03-02 22:10, Gustavo A. R. Silva wrote:
> Hi all,
> 
> The following piece of code in drivers/net/wireless/mediatek/mt76/mt7603/mac.c
> is missing a variable assignment before line 1058.  Notice that there
> is a potential execution path in which variable *i* is compared against
> magic number 15 at line 1075 without being initialized previously
> (this was reported by Coverity):
> 
> 1055 out:
> 1056         final_rate_flags = info->status.rates[final_idx].flags;
> 1057 
> 1058         switch (FIELD_GET(MT_TX_RATE_MODE, final_rate)) {
> 1059         case MT_PHY_TYPE_CCK:
> 1060                 cck = true;
> 1061                 /* fall through */
> 1062         case MT_PHY_TYPE_OFDM:
> 1063                 if (dev->mt76.chandef.chan->band == NL80211_BAND_5GHZ)
> 1064                         sband = &dev->mt76.sband_5g.sband;
> 1065                 else
> 1066                         sband = &dev->mt76.sband_2g.sband;
> 1067                 final_rate &= GENMASK(5, 0);
> 1068                 final_rate = mt7603_get_rate(dev, sband, final_rate, cck);
> 1069                 final_rate_flags = 0;
> 1070                 break;
> 1071         case MT_PHY_TYPE_HT_GF:
> 1072         case MT_PHY_TYPE_HT:
> 1073                 final_rate_flags |= IEEE80211_TX_RC_MCS;
> 1074                 final_rate &= GENMASK(5, 0);
> 1075                 if (i > 15)
> 1076                         return false;
> 1077                 break;
> 1078         default:
> 1079                 return false;
> 1080         }
> 
> My guess is that such missing assignment should be something similar
> to the one at line 566:
> 
> 	i = FIELD_GET(MT_RXV1_TX_RATE, rxdg0);
> 
> but I'm not sure what the proper arguments for macro FIELD_GET should
> be.
> 
> This code was introduced by commit c8846e1015022d2531ac4c895783e400b3e5babe
> 
> What do you think?
Thanks for reporting this. The fix is simpler than that, the check
should be: if (final_rate > 15)
I will send a fix.

- Felix