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Subject: Re: [PATCH] ath10k: htt_rx: Fix signedness bug in
 ath10k_update_per_peer_tx_stats
To:     Ben Greear <greearb@candelatech.com>,
        Kalle Valo <kvalo@codeaurora.org>,
        "David S. Miller" <davem@davemloft.net>
Cc:     ath10k@lists.infradead.org, linux-wireless@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20181005184245.GA11700@embeddedor.com>
 <3a55bec6-d20d-f500-e741-b228a86b7117@candelatech.com>
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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Date:   Fri, 5 Oct 2018 21:14:27 +0200
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On 10/5/18 9:09 PM, Ben Greear wrote:
> On 10/05/2018 11:42 AM, Gustavo A. R. Silva wrote:
>> Currently, the error handling for the call to function
>> ath10k_get_legacy_rate_idx() doesn't work because
>> *rate_idx* is of type u8 (8 bits, unsigned), which
>> makes it impossible for it to hold a value less
>> than 0.
>>
>> Fix this by changing the type of variable *rate_idx*
>> to s8 (8 bits, signed).
> 
> There are more than 127 rates, are you sure this is doing
> what you want?
> 

Based on the following function, rate_idx can only hold values from 0 to 11

static inline int ath10k_get_legacy_rate_idx(struct ath10k *ar, u8 rate)
{
        static const u8 legacy_rates[] = {1, 2, 5, 11, 6, 9, 12,
                                          18, 24, 36, 48, 54};
        int i;

        for (i = 0; i < ARRAY_SIZE(legacy_rates); i++) {
                if (rate == legacy_rates[i])
                        return i;
        }

        ath10k_warn(ar, "Invalid legacy rate %hhd peer stats", rate);
        return -EINVAL;
}

Thanks
--
Gustavo

> Thanks,
> Ben
> 
>>
>> Addresses-Coverity-ID: 1473914 ("Unsigned compared against 0")
>> Fixes: 0189dbd71cbd ("ath10k: get the legacy rate index to update the txrate table")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
>> ---
>> ?drivers/net/wireless/ath/ath10k/htt_rx.c | 3 ++-
>> ?1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/wireless/ath/ath10k/htt_rx.c b/drivers/net/wireless/ath/ath10k/htt_rx.c
>> index f240525..edd0e74 100644
>> --- a/drivers/net/wireless/ath/ath10k/htt_rx.c
>> +++ b/drivers/net/wireless/ath/ath10k/htt_rx.c
>> @@ -2753,7 +2753,8 @@ ath10k_update_per_peer_tx_stats(struct ath10k *ar,
>> ???????????????? struct ath10k_per_peer_tx_stats *peer_stats)
>> ?{
>> ???? struct ath10k_sta *arsta = (struct ath10k_sta *)sta->drv_priv;
>> -??? u8 rate = 0, rate_idx = 0, sgi;
>> +??? u8 rate = 0, sgi;
>> +??? s8 rate_idx = 0;
>> ???? struct rate_info txrate;
>>
>> ???? lockdep_assert_held(&ar->data_lock);
>>
> 
>