Message ID | 20130822135342.GC30722@order.stressinduktion.org |
---|---|
State | Not Applicable, archived |
Delegated to: | David Miller |
Headers | show |
On Thu, Aug 22, 2013 at 03:53:42PM +0200, Hannes Frederic Sowa wrote: > On Thu, Aug 22, 2013 at 12:47:24PM +0200, Steffen Klassert wrote: > > Hannes, > > > > I have two problematic commits from you in the ipsec tree. The first one is: > > > > commit 0ea9d5e3e (xfrm: introduce helper for safe determination of mtu) > > > > This breakes pmtu discovery for IPv4 because now we use the device mtu > > instead of the reduced IPsec mtu in xfrm4_tunnel_check_size() if a IPv4 > > socket is at the skb. > > I am currently testing this following patch. It should restore old behavior > for ipv4 sockets. > > diff --git a/include/net/xfrm.h b/include/net/xfrm.h > index ac5b025..65d3529 100644 > --- a/include/net/xfrm.h > +++ b/include/net/xfrm.h > @@ -1730,8 +1730,6 @@ static inline int xfrm_skb_dst_mtu(struct sk_buff *skb) > > if (sk && skb->protocol == htons(ETH_P_IPV6)) > return ip6_skb_dst_mtu(skb); > - else if (sk && skb->protocol == htons(ETH_P_IP)) > - return ip_skb_dst_mtu(skb); > return dst_mtu(skb_dst(skb)); > } This looks still fragile. xfrm_skb_dst_mtu() is called from __xfrm6_output() and from xfrm4_tunnel_check_size(). We will have the same bug again as soon as somebody thinks that it is save to call it from xfrm6_tunnel_check_size() too. So I think it is better not to call it from xfrm4_tunnel_check_size(). Also, why do we need xfrm_skb_dst_mtu() at all? When it is called from __xfrm6_output(), we know that this is IPv6. So we can call ip6_skb_dst_mtu() directly as it was before your change. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hello! On Fri, Aug 23, 2013 at 10:58:07AM +0200, Steffen Klassert wrote: > On Thu, Aug 22, 2013 at 03:53:42PM +0200, Hannes Frederic Sowa wrote: > > On Thu, Aug 22, 2013 at 12:47:24PM +0200, Steffen Klassert wrote: > > > Hannes, > > > > > > I have two problematic commits from you in the ipsec tree. The first one is: > > > > > > commit 0ea9d5e3e (xfrm: introduce helper for safe determination of mtu) > > > > > > This breakes pmtu discovery for IPv4 because now we use the device mtu > > > instead of the reduced IPsec mtu in xfrm4_tunnel_check_size() if a IPv4 > > > socket is at the skb. > > > > I am currently testing this following patch. It should restore old behavior > > for ipv4 sockets. > > > > diff --git a/include/net/xfrm.h b/include/net/xfrm.h > > index ac5b025..65d3529 100644 > > --- a/include/net/xfrm.h > > +++ b/include/net/xfrm.h > > @@ -1730,8 +1730,6 @@ static inline int xfrm_skb_dst_mtu(struct sk_buff *skb) > > > > if (sk && skb->protocol == htons(ETH_P_IPV6)) > > return ip6_skb_dst_mtu(skb); > > - else if (sk && skb->protocol == htons(ETH_P_IP)) > > - return ip_skb_dst_mtu(skb); > > return dst_mtu(skb_dst(skb)); > > } > > This looks still fragile. xfrm_skb_dst_mtu() is called from > __xfrm6_output() and from xfrm4_tunnel_check_size(). > We will have the same bug again as soon as somebody thinks that > it is save to call it from xfrm6_tunnel_check_size() too. So I > think it is better not to call it from xfrm4_tunnel_check_size(). Hm, I don't think I can follow you completly here. I searched for allocations of ipv6 skbs (where they originated from a socket) and checked these allocations also initialize the skb->protocol field (the second patch). I wonder if ip6_skb_dst_mtu was correct all along and if we should just switch to dst_mtu(skb_dst(skb)) in all cases? > Also, why do we need xfrm_skb_dst_mtu() at all? When it is called > from __xfrm6_output(), we know that this is IPv6. So we can call > ip6_skb_dst_mtu() directly as it was before your change. The problem was that ip6_skb_dst_mtu dereferences the ipv6_pinfo socket to check for IPV6_PMTUDISC_PROBE. If IPv4 is encapsulated in IPv6 and the packet originated from the same host (sk != NULL) we call down to ip6_skb_dst_mtu. This function checks that ipv6_pinfo is not NULL, so it worked by accident currently. My plan would be to check that all IPv4 skb allocations use the correct skb->protocol, too, or if we can use the skb->inner_protocol field to mark packets in the tunnel drivers from which protocol they originated. Greetings, Hannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Aug 23, 2013 at 01:03:23PM +0200, Hannes Frederic Sowa wrote: > Hello! > > On Fri, Aug 23, 2013 at 10:58:07AM +0200, Steffen Klassert wrote: > > On Thu, Aug 22, 2013 at 03:53:42PM +0200, Hannes Frederic Sowa wrote: > > > On Thu, Aug 22, 2013 at 12:47:24PM +0200, Steffen Klassert wrote: > > > > Hannes, > > > > > > > > I have two problematic commits from you in the ipsec tree. The first one is: > > > > > > > > commit 0ea9d5e3e (xfrm: introduce helper for safe determination of mtu) > > > > > > > > This breakes pmtu discovery for IPv4 because now we use the device mtu > > > > instead of the reduced IPsec mtu in xfrm4_tunnel_check_size() if a IPv4 > > > > socket is at the skb. > > > > > > I am currently testing this following patch. It should restore old behavior > > > for ipv4 sockets. > > > > > > diff --git a/include/net/xfrm.h b/include/net/xfrm.h > > > index ac5b025..65d3529 100644 > > > --- a/include/net/xfrm.h > > > +++ b/include/net/xfrm.h > > > @@ -1730,8 +1730,6 @@ static inline int xfrm_skb_dst_mtu(struct sk_buff *skb) > > > > > > if (sk && skb->protocol == htons(ETH_P_IPV6)) > > > return ip6_skb_dst_mtu(skb); > > > - else if (sk && skb->protocol == htons(ETH_P_IP)) > > > - return ip_skb_dst_mtu(skb); > > > return dst_mtu(skb_dst(skb)); > > > } > > > > This looks still fragile. xfrm_skb_dst_mtu() is called from > > __xfrm6_output() and from xfrm4_tunnel_check_size(). > > We will have the same bug again as soon as somebody thinks that > > it is save to call it from xfrm6_tunnel_check_size() too. So I > > think it is better not to call it from xfrm4_tunnel_check_size(). > > Hm, I don't think I can follow you completly here. I searched for allocations > of ipv6 skbs (where they originated from a socket) and checked these > allocations also initialize the skb->protocol field (the second patch). > > I wonder if ip6_skb_dst_mtu was correct all along and if we should just > switch to dst_mtu(skb_dst(skb)) in all cases? Ok, I got it. How about just checking in __xfrm6_output if we actually have a packet originated from an IPv6 socket so that we only replace the original call to ip6_skb_dst_mtu(skb)? > > > Also, why do we need xfrm_skb_dst_mtu() at all? When it is called > > from __xfrm6_output(), we know that this is IPv6. So we can call > > ip6_skb_dst_mtu() directly as it was before your change. > > The problem was that ip6_skb_dst_mtu dereferences the ipv6_pinfo socket to > check for IPV6_PMTUDISC_PROBE. If IPv4 is encapsulated in IPv6 and the packet > originated from the same host (sk != NULL) we call down to ip6_skb_dst_mtu. > This function checks that ipv6_pinfo is not NULL, so it worked by accident > currently. > > My plan would be to check that all IPv4 skb allocations use the correct > skb->protocol, too, or if we can use the skb->inner_protocol field to mark > packets in the tunnel drivers from which protocol they originated. Btw. this also let's us refer to the wrong mtu in case of an v4-mapped v6 socket transmitting over a address family changing tunnel over ipsec. Greetings, Hannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/net/xfrm.h b/include/net/xfrm.h index ac5b025..65d3529 100644 --- a/include/net/xfrm.h +++ b/include/net/xfrm.h @@ -1730,8 +1730,6 @@ static inline int xfrm_skb_dst_mtu(struct sk_buff *skb) if (sk && skb->protocol == htons(ETH_P_IPV6)) return ip6_skb_dst_mtu(skb); - else if (sk && skb->protocol == htons(ETH_P_IP)) - return ip_skb_dst_mtu(skb); return dst_mtu(skb_dst(skb)); }