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Date:   Sun, 20 Jan 2019 11:32:13 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     f6bvp <f6bvp@...e.fr>
Cc:     linux-hams <linux-hams@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        David Miller <davem@...emloft.net>,
        Linux Netdev List <netdev@...r.kernel.org>,
        n1uro@...ro.ampr.org, C Schuman <k4gbb1@...arqmail.com>
Subject: Re: [PATCH] NET:AX25:ROSE NULL ax25_cb kernel panic

On Sun, Jan 20, 2019 at 10:58 AM f6bvp <f6bvp@...e.fr> wrote:
>
> Hi,
>
> Dmitry wrote:
>
> >Please also add:
> >Reported-by: syzbot+1a2c456a1ea08fa5b5f7@...kaller.appspotmail.com
>
> I did mention syzbot report but without the exact reference, thanks.
>
> >It's this report we are fixing, right?
> >https://syzkaller.appspot.com/bug?id=fd0b0b00fc26abb4b35663a0e2f1c91d8e6e5725
>
> Yes exactly !
> This is a long date well know bug I reported two years ago.

Then, well, I don't know, we either can leave syzbot as reporter if
you don't mind. Or don't include it as supports other means to
associate reports with fixes (#syz fix tag in email). The goal of
associating fixes with reports is to "close" bugs and get them off the
dashboard:
https://syzkaller.appspot.com/#upstream-open
Otherwise it turns into unuseful pile of bugs.



> Bernard
>
>
> On Sat, Jan 19, 2019 at 11:58 AM f6bvp <f6bvp@...e.fr> wrote:
> >
> >
> > [PATCH] [ROSE] NULL ax25_cb kernel panic
> >
> > When an internally generated frame is handled by rose_xmit(),
> > rose_route_frame() is called:
> >
> >         if (!rose_route_frame(skb, NULL)) {
> >                 dev_kfree_skb(skb);
> >                 stats->tx_errors++;
> >                 return NETDEV_TX_OK;
> >         }
> >
> > We have the same code sequence in Net/Rom where an internally generated
> > frame is handled by nr_xmit() calling nr_route_frame(skb, NULL).
> > However, in this function NULL argument is tested while it is not in
> > rose_route_frame().
> > Then kernel panic occurs later on when calling ax25cmp() with a NULL
> > ax25_cb argument as reported many times and recently with syzbot.
> >
> > We need to test if ax25 is NULL before using it.
> >
> > Here is the patch:
> >
> > diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
> > index 77e9f85a2c92..7f075255a372 100644
> > --- a/net/rose/rose_route.c
> > +++ b/net/rose/rose_route.c
> > @@ -850,6 +850,7 @@ void rose_link_device_down(struct net_device *dev)
> >
> >  /*
> >   *     Route a frame to an appropriate AX.25 connection.
> > + *     a NULL ax25_cb indicates an internally generated frame.
> >   */
> >  int rose_route_frame(struct sk_buff *skb, ax25_cb *ax25)
> >  {
> > @@ -867,6 +868,10 @@ int rose_route_frame(struct sk_buff *skb, ax25_cb
> > *ax25)
> >
> >         if (skb->len < ROSE_MIN_LEN)
> >                 return res;
> > +
> > +       if (!ax25)
> > +               return rose_loopback_queue(skb, NULL);
> > +
> >         frametype = skb->data[2];
> >         lci = ((skb->data[0] << 8) & 0xF00) + ((skb->data[1] << 0) &
> 0x0FF);
> >         if (frametype == ROSE_CALL_REQUEST &&
> >
> > Signed-off-by: Bernard Pidoux, f6bvp <f6bvp@...e.fr>
>
> Please also add:
>
> Reported-by: syzbot+1a2c456a1ea08fa5b5f7@...kaller.appspotmail.com
>
> It's this report we are fixing, right?
> https://syzkaller.appspot.com/bug?id=fd0b0b00fc26abb4b35663a0e2f1c91d8e6e5725

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