Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.31 as permitted sender) client-ip=23.128.96.31;
Message-ID: <9daf8509e39cd20d9d806afdb425ad43af037f8d.camel@redhat.com>
Subject: Re: [PATCH net] ipv4: ip_gre: Handle skb_pull() failure in
 ipgre_xmit()
From:   Paolo Abeni <pabeni@redhat.com>
To:     Eric Dumazet <edumazet@google.com>,
        Shigeru Yoshida <syoshida@redhat.com>
Cc:     davem@davemloft.net, dsahern@kernel.org, kuba@kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Tue, 28 Nov 2023 16:51:09 +0100
In-Reply-To: <CANn89iKcstKYWoqUCXHO__7PfVRMFNnN5nRQVCTAADvFbcJRww@mail.gmail.com>
References: <20231126151652.372783-1-syoshida@redhat.com>
         <CANn89iKcstKYWoqUCXHO__7PfVRMFNnN5nRQVCTAADvFbcJRww@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) 
MIME-Version: 1.0
Precedence: bulk

On Tue, 2023-11-28 at 16:45 +0100, Eric Dumazet wrote:
> On Sun, Nov 26, 2023 at 4:17=E2=80=AFPM Shigeru Yoshida <syoshida@redhat.=
com> wrote:
> >=20
> > In ipgre_xmit(), skb_pull() may fail even if pskb_inet_may_pull() retur=
ns
> > true. For example, applications can create a malformed packet that caus=
es
> > this problem with PF_PACKET.
> >=20
> > This patch fixes the problem by dropping skb and returning from the
> > function if skb_pull() fails.
> >=20
> > Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
> > Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> > ---
> >  net/ipv4/ip_gre.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >=20
> > diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> > index 22a26d1d29a0..95efa97cb84b 100644
> > --- a/net/ipv4/ip_gre.c
> > +++ b/net/ipv4/ip_gre.c
> > @@ -643,7 +643,8 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
> >                 /* Pull skb since ip_tunnel_xmit() needs skb->data poin=
ting
> >                  * to gre header.
> >                  */
> > -               skb_pull(skb, tunnel->hlen + sizeof(struct iphdr));
> > +               if (!skb_pull(skb, tunnel->hlen + sizeof(struct iphdr))=
)
> > +                       goto free_skb;
> >                 skb_reset_mac_header(skb);
> >=20
> >                 if (skb->ip_summed =3D=3D CHECKSUM_PARTIAL &&
> > --
>=20
>=20
> I have syszbot reports with an actual repro for this one.

Could you please share them? I could not find easily the reports in
https://syzkaller.appspot.com/upstream

Thanks,

Paolo