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

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Date:   Fri, 3 Apr 2020 17:39:34 -0700
From:   Sonny Sasaka <sonnysasaka@...omium.org>
To:     Alain Michaud <alainmichaud@...gle.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        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>
Subject: Re: [PATCH] Bluetooth: Simplify / fix return values from tk_request

The patch looks good to me. Agreed with Guenter's assessment, I made a
mistake in the original patch by not being consistent with the
function contract.

On Fri, Apr 3, 2020 at 9:57 AM Alain Michaud <alainmichaud@...gle.com> wrote:
>
> On Fri, Apr 3, 2020 at 12:43 PM Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > 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.
> Agreed, the conventions aren't clear here.  I'll differ to Marcel to
> provide guidance in this case where as a long term solution might
> increase the scope of this patch beyond what would be reasonable.
> >
> > Guenter
> >
> > >>                 set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
> > >>                 return 0;
> > >>         }
> > >> --
> > >> 2.17.1
> > >>
> > >
> > > Thanks,
> > > Alain
> > >
> >