Re: [syzbot] general protection fault in sctp_rcv

From: Xin Long <lucien.xin@gmail.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: syzbot <syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com>,
	davem <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"linux-sctp @ vger . kernel . org" <linux-sctp@vger.kernel.org>,
	Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
	network dev <netdev@vger.kernel.org>,
	Neil Horman <nhorman@tuxdriver.com>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Vlad Yasevich <vyasevich@gmail.com>
Subject: Re: [syzbot] general protection fault in sctp_rcv
Date: Sun, 3 Oct 2021 17:43:34 +0800	[thread overview]
Message-ID: <CADvbK_fso7ZLnOwcZbvoSORErT4BG0JwGGxdKg237e_wvv7Usw@mail.gmail.com> (raw)
In-Reply-To: <20210924171412.GF2083@kadam>

On Sat, Sep 25, 2021 at 1:14 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Thu, Sep 23, 2021 at 12:34:42PM +0300, Dan Carpenter wrote:
> > On Wed, Sep 22, 2021 at 05:18:29PM +0800, Xin Long wrote:
> > > On Tue, Sep 21, 2021 at 12:09 PM syzbot
> > > <syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com> wrote:
> > > >
> > > > Hello,
> > > >
> > > > syzbot found the following issue on:
> > > >
> > > > HEAD commit:    98dc68f8b0c2 selftests: nci: replace unsigned int with int
> > > > git tree:       net
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=11fd443d300000
> > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=c31c0936547df9ea
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=581aff2ae6b860625116
> > > > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > > >
> > > > Unfortunately, I don't have any reproducer for this issue yet.
> > > >
> > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > Reported-by: syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com
> > > >
> > > > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> > > > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> > > > CPU: 0 PID: 11205 Comm: kworker/0:12 Not tainted 5.14.0-syzkaller #0
> > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > > > Workqueue: ipv6_addrconf addrconf_dad_work
> > > > RIP: 0010:sctp_rcv_ootb net/sctp/input.c:705 [inline]
> > > by anyway, checking if skb_header_pointer() return NULL is always needed:
> > > @@ -702,7 +702,7 @@ static int sctp_rcv_ootb(struct sk_buff *skb)
> > >                 ch = skb_header_pointer(skb, offset, sizeof(*ch), &_ch);
> > >
> > >                 /* Break out if chunk length is less then minimal. */
> > > -               if (ntohs(ch->length) < sizeof(_ch))
> > > +               if (!ch || ntohs(ch->length) < sizeof(_ch))
> > >                         break;
> > >
> >
> > The skb_header_pointer() function is annotated as __must_check but that
> > only means you have to use the return value.  These things would be
> > better as a Coccinelle or Smatch check.
> >
> > I will create a Smatch warning for this.
>
> These are the Smatch warnings for this:
>
> net/sctp/input.c:705 sctp_rcv_ootb() error: skb_header_pointer() returns NULL
> net/ipv6/netfilter/ip6t_rt.c:111 rt_mt6() error: skb_header_pointer() returns NULL
> net/ipv4/icmp.c:1076 icmp_build_probe() error: skb_header_pointer() returns NULL
> net/ipv4/icmp.c:1089 icmp_build_probe() error: skb_header_pointer() returns NULL
Will post follow-ups for rt_mt6() and icmp_build_probe() too.

Thanks!
>
> regards,
> dan carpenter
>