From: "Starke, Daniel" <daniel.starke@siemens.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
"jirislaby@kernel.org" <jirislaby@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 16/20] tty: n_gsm: fix invalid command/response bit check for UI/UIH frames
Date: Tue, 19 Apr 2022 07:10:43 +0000 [thread overview]
Message-ID: <AM4PR1001MB1378879B82FF126255EFB099E0F29@AM4PR1001MB1378.EURPRD10.PROD.OUTLOOK.COM> (raw)
> 42:21AM -0700, D. Starke wrote:
> > From: Daniel Starke <daniel.starke@siemens.com>
> >
> > n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010.
> > See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1516
> > The changes from 07.010 to 27.010 are non-functional. Therefore, I
> > refer to the newer 27.010 here. Chapter 5.4.3.1 states the CR bit in
> > UI and UIH frames shall always be set 1 by the initiator and 0 by the responder.
>
> This has nothing to do with the change you made here.
>
>
> > Currently, gsm_queue() has a pre-processor gated (excluded) check
> > which treats all frames that conform to the standard as malformed frames.
> > Remove this optional code to avoid confusion and possible breaking
> > changes in case that someone includes it.
>
> Again, nothing to do with the code change.
Including this code (i.e. with #if 1) will treat every correct UI/UIH frame
as invalid, because the cr flag is always set to 1 for those frames
(as mentioned in chapter 5.4.3.1 of the standard). This is obviously wrong.
> >
> > Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
>
> This "fixes" nothing :(
What is the correct way to handle the removal of such dead and obviously
wrong code?
> > Cc: stable@vger.kernel.org
>
> How is commenting out unused code a stable backport requirement?
True, it does not change the behavior but it fixes a commit which is also
present in the current stable release. I was unsure how to handle this
case. I will remove the backport remark.
> > Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
> > ---
> > drivers/tty/n_gsm.c | 4 ----
> > 1 file changed, 4 deletions(-)
> >
> > diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index
> > e9a7d9483c1f..f4ec48c0d6d7 100644
> > --- a/drivers/tty/n_gsm.c
> > +++ b/drivers/tty/n_gsm.c
> > @@ -1896,10 +1896,6 @@ static void gsm_queue(struct gsm_mux *gsm)
> > case UI|PF:
> > case UIH:
> > case UIH|PF:
> > -#if 0
> > - if (cr)
> > - goto invalid;
> > -#endif
>
> All you are doing is cleaning up dead code. Not a big deal, and not
> worth all the text above to confuse people :(
As mentioned above, this is not only dead but also wrong code. I tried to
elaborate the reason for it being wrong code in the text above.
Best regards,
Daniel Starke
next reply other threads:[~2022-04-19 7:10 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-19 7:10 Starke, Daniel [this message]
2022-04-19 7:26 ` [PATCH 16/20] tty: n_gsm: fix invalid command/response bit check for UI/UIH frames Greg KH
-- strict thread matches above, loose matches on Subject: below --
2022-04-14 9:42 [PATCH 01/20] tty: n_gsm: fix missing mux reset on config change at responder D. Starke
2022-04-14 9:42 ` [PATCH 16/20] tty: n_gsm: fix invalid command/response bit check for UI/UIH frames D. Starke
2022-04-15 6:31 ` Greg KH
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