From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756629Ab3DXPOJ (ORCPT ); Wed, 24 Apr 2013 11:14:09 -0400 Received: from mail-pd0-f171.google.com ([209.85.192.171]:56139 "EHLO mail-pd0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756436Ab3DXPOH (ORCPT ); Wed, 24 Apr 2013 11:14:07 -0400 Message-ID: <1366816444.8964.72.camel@edumazet-glaptop> Subject: Re: gre: Support GRE over IPv6 From: Eric Dumazet To: Geert Uytterhoeven Cc: Dmitry Kozlov , "David S. Miller" , netdev@vger.kernel.org, Linux Kernel Development Date: Wed, 24 Apr 2013 08:14:04 -0700 In-Reply-To: References: <20121002205219.7C3BD340556@ra.kernel.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 8bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-04-24 at 14:23 +0200, Geert Uytterhoeven wrote: > On Tue, 2 Oct 2012, Linux Kernel Mailing List wrote: > > Gitweb: http://git.kernel.org/linus/;a=commit;h=c12b395a46646bab69089ce7016ac78177f6001f > > Commit: c12b395a46646bab69089ce7016ac78177f6001f > > Parent: b7bc2a5b5bd99b216c3e5fe68c7f45c684ab5745 > > Author: xeb@mail.ru > > AuthorDate: Fri Aug 10 00:51:50 2012 +0000 > > Committer: David S. Miller > > CommitDate: Tue Aug 14 14:28:32 2012 -0700 > > > > gre: Support GRE over IPv6 > > > > GRE over IPv6 implementation. > > > > Signed-off-by: Dmitry Kozlov > > Signed-off-by: David S. Miller > > > --- /dev/null > > +++ b/net/ipv6/ip6_gre.c > > > +static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb, > > + struct net_device *dev, > > + __u8 dsfield, > > + struct flowi6 *fl6, > > + int encap_limit, > > + __u32 *pmtu) > > +{ > > + struct net *net = dev_net(dev); > > + struct ip6_tnl *tunnel = netdev_priv(dev); > > + struct net_device *tdev; /* Device to other host */ > > + struct ipv6hdr *ipv6h; /* Our new IP header */ > > + unsigned int max_headroom; /* The extra header space needed */ > > max_headroom is not initialized > > > + mtu = dst_mtu(dst) - sizeof(*ipv6h); > > + if (encap_limit >= 0) { > > + max_headroom += 8; > > Hence gcc (4.1.2) rightfully complains: > > net/ipv6/ip6_gre.c: In function ‘ip6gre_xmit2’: > net/ipv6/ip6_gre.c:713: warning: ‘max_headroom’ is used uninitialized in this function > > However, initializing max_headroom to zero at the top, or replacing the line > above by "max_headroom = 8" doesn't seem to be the right fix... > > > + mtu -= 8; > > + } > > + if (mtu < IPV6_MIN_MTU) > > + mtu = IPV6_MIN_MTU; > > + if (skb_dst(skb)) > > + skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu); > > + if (skb->len > mtu) { > > + *pmtu = mtu; > > + err = -EMSGSIZE; > > + goto tx_err_dst_release; > > + } > > + > > + if (tunnel->err_count > 0) { > > + if (time_before(jiffies, > > + tunnel->err_time + IP6TUNNEL_ERR_TIMEO)) { > > + tunnel->err_count--; > > + > > + dst_link_failure(skb); > > + } else > > + tunnel->err_count = 0; > > + } > > + > > + max_headroom = LL_RESERVED_SPACE(tdev) + gre_hlen + dst->header_len; > > ... as max_headroom is overwritten here anyway? > > So something is really wrong here. What is the right fix? > > This issue is present in current mainline as of v3.7. I would use following fix. Can you provide an official patch ? diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index d3ddd84..150d17d 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -620,7 +620,7 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb, struct ip6_tnl *tunnel = netdev_priv(dev); struct net_device *tdev; /* Device to other host */ struct ipv6hdr *ipv6h; /* Our new IP header */ - unsigned int max_headroom; /* The extra header space needed */ + unsigned int max_headroom = 0; /* The extra header space needed */ int gre_hlen; struct ipv6_tel_txoption opt; int mtu; @@ -693,7 +693,7 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb, tunnel->err_count = 0; } - max_headroom = LL_RESERVED_SPACE(tdev) + gre_hlen + dst->header_len; + max_headroom += LL_RESERVED_SPACE(tdev) + gre_hlen + dst->header_len; if (skb_headroom(skb) < max_headroom || skb_shared(skb) || (skb_cloned(skb) && !skb_clone_writable(skb, 0))) {