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Date:   Fri, 12 Aug 2022 22:41:35 +0300
Message-Id: <CM4B165JCMGL.1LA0ST6YL7QAS@Arch-Desktop>
To:     "Starke, Daniel" <daniel.starke@siemens.com>
Cc:     "jirislaby@kernel.org" <jirislaby@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-kernel-mentees@lists.linuxfoundation.org" 
        <linux-kernel-mentees@lists.linuxfoundation.org>,
        "skhan@linuxfoundation.org" <skhan@linuxfoundation.org>,
        "paskripkin@gmail.com" <paskripkin@gmail.com>,
        "syzbot+e3563f0c94e188366dbb@syzkaller.appspotmail.com" 
        <syzbot+e3563f0c94e188366dbb@syzkaller.appspotmail.com>,
        "Greg KH" <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in
 gsmld_attach_gsm()
From:   "Mazin Al Haddad" <mazinalhaddad05@gmail.com>
References: <DB9PR10MB58813E33D3516BAB526156B1E0659@DB9PR10MB5881.EURPRD10.PROD.OUTLOOK.COM>
In-Reply-To: <DB9PR10MB58813E33D3516BAB526156B1E0659@DB9PR10MB5881.EURPRD10.PROD.OUTLOOK.COM>
Precedence: bulk

On Wed Aug 10, 2022 at 12:08 PM +03, Starke, Daniel wrote:
> > Fix this by setting the gsm->receive() function when the line=20
> > discipline is being attached to the terminal device, inside=20
> > gsmld_attach_gsm(). This will guarantee that the function is assigned=
=20
> > and a call to TIOCSTI, which calls gsmld_receive_buf(), will not
> > reference a null pointer.
>
> In my opinion there are only two possible ways to fix this:
> a) Move the gsm->receive initialization from gsm_activate_mux() to
> gsmld_attach_gsm().
> b) Avoid calling gsm->receive in gsmld_receive_buf() if not initialized.
>
> The current code might assume that gsm->receive is only called after MUX
> activation. Therefore, variant a) may break the code in other places.
> I see no need to initialize gsm->receive in gsm_activate_mux() and
> gsmld_attach_gsm().

Thanks for the feedback! I will send a v2 patch that implements a check
shortly.=20