netdev - Re: [PATCH] Bluetooth: Simplify / fix return values from tk

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Date:   Fri, 3 Apr 2020 09:42:57 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Alain Michaud <alainmichaud@...gle.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        BlueZ <linux-bluetooth@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sonny Sasaka <sonnysasaka@...omium.org>
Subject: Re: [PATCH] Bluetooth: Simplify / fix return values from tk_request

On 4/3/20 8:13 AM, Alain Michaud wrote:
> Hi Guenter/Marcel,
> 
> 
> On Fri, Apr 3, 2020 at 11:03 AM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> Some static checker run by 0day reports a variableScope warning.
>>
>> net/bluetooth/smp.c:870:6: warning:
>>         The scope of the variable 'err' can be reduced. [variableScope]
>>
>> There is no need for two separate variables holding return values.
>> Stick with the existing variable. While at it, don't pre-initialize
>> 'ret' because it is set in each code path.
>>
>> tk_request() is supposed to return a negative error code on errors,
>> not a bluetooth return code. The calling code converts the return
>> value to SMP_UNSPECIFIED if needed.
>>
>> Fixes: 92516cd97fd4 ("Bluetooth: Always request for user confirmation for Just Works")
>> Cc: Sonny Sasaka <sonnysasaka@...omium.org>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>>  net/bluetooth/smp.c | 9 ++++-----
>>  1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
>> index d0b695ee49f6..30e8626dd553 100644
>> --- a/net/bluetooth/smp.c
>> +++ b/net/bluetooth/smp.c
>> @@ -854,8 +854,7 @@ static int tk_request(struct l2cap_conn *conn, u8 remote_oob, u8 auth,
>>         struct l2cap_chan *chan = conn->smp;
>>         struct smp_chan *smp = chan->data;
>>         u32 passkey = 0;
>> -       int ret = 0;
>> -       int err;
>> +       int ret;
>>
>>         /* Initialize key for JUST WORKS */
>>         memset(smp->tk, 0, sizeof(smp->tk));
>> @@ -887,12 +886,12 @@ static int tk_request(struct l2cap_conn *conn, u8 remote_oob, u8 auth,
>>         /* If Just Works, Continue with Zero TK and ask user-space for
>>          * confirmation */
>>         if (smp->method == JUST_WORKS) {
>> -               err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
>> +               ret = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
>>                                                 hcon->type,
>>                                                 hcon->dst_type,
>>                                                 passkey, 1);
>> -               if (err)
>> -                       return SMP_UNSPECIFIED;
>> +               if (ret)
>> +                       return ret;
> I think there may be some miss match between expected types of error
> codes here.  The SMP error code type seems to be expected throughout
> this code base, so this change would propagate a potential negative
> value while the rest of the SMP protocol expects strictly positive
> error codes.
> 

Up to the patch introducing the SMP_UNSPECIFIED return value, tk_request()
returned negative error codes, and all callers convert it to SMP_UNSPECIFIED.

If tk_request() is supposed to return SMP_UNSPECIFIED on error, it should
be returned consistently, and its callers don't have to convert it again.

Guenter

>>                 set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
>>                 return 0;
>>         }
>> --
>> 2.17.1
>>
> 
> Thanks,
> Alain
>