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SubjectRe: [PATCH 4.4 002/193] net: replace dst_cache ip6_tunnel implementation with the generic one
On Tue, Feb 27, 2018 at 09:05:01AM +0100, Michal Kubecek wrote:
> On Fri, Feb 23, 2018 at 07:23:55PM +0100, Greg Kroah-Hartman wrote:
> > 4.4-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Paolo Abeni <pabeni@redhat.com>
> >
> > commit 607f725f6f7d5ec3759fbc16224afb60e2152a5b upstream.
> >
> > This also fix a potential race into the existing tunnel code, which
> > could lead to the wrong dst to be permanenty cached:
> >
> > CPU1: CPU2:
> > <xmit on ip6_tunnel>
> > <cache lookup fails>
> > dst = ip6_route_output(...)
> > <tunnel params are changed via nl>
> > dst_cache_reset() // no effect,
> > // the cache is empty
> > dst_cache_set() // the wrong dst
> > // is permanenty stored
> > // into the cache
> >
> > With the new dst implementation the above race is not possible
> > since the first cache lookup after dst_cache_reset will fail due
> > to the timestamp check
> >
> > Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> > Suggested-and-acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> > Signed-off-by: David S. Miller <davem@davemloft.net>
> > Signed-off-by: Manoj Boopathi Raj <manojboopathi@google.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> >
> > ---
> ...
> > --- a/net/ipv6/ip6_gre.c
> > +++ b/net/ipv6/ip6_gre.c
> ...
> > @@ -1053,7 +962,6 @@ static int ip6_tnl_xmit2(struct sk_buff
> > struct ipv6_tel_txoption opt;
> > struct dst_entry *dst = NULL, *ndst = NULL;
> > struct net_device *tdev;
> > - bool use_cache = false;
> > int mtu;
> > unsigned int max_headroom = sizeof(struct ipv6hdr);
> > u8 proto;
> > @@ -1061,39 +969,28 @@ static int ip6_tnl_xmit2(struct sk_buff
> >
> > /* NBMA tunnel */
> > if (ipv6_addr_any(&t->parms.raddr)) {
> > - if (skb->protocol == htons(ETH_P_IPV6)) {
> > - struct in6_addr *addr6;
> > - struct neighbour *neigh;
> > - int addr_type;
> > -
> > - if (!skb_dst(skb))
> > - goto tx_err_link_failure;
> > -
> > - neigh = dst_neigh_lookup(skb_dst(skb),
> > - &ipv6_hdr(skb)->daddr);
> > - if (!neigh)
> > - goto tx_err_link_failure;
> > + struct in6_addr *addr6;
> > + struct neighbour *neigh;
> > + int addr_type;
> > +
> > + if (!skb_dst(skb))
> > + goto tx_err_link_failure;
> >
> > - addr6 = (struct in6_addr *)&neigh->primary_key;
> > - addr_type = ipv6_addr_type(addr6);
> > + neigh = dst_neigh_lookup(skb_dst(skb),
> > + &ipv6_hdr(skb)->daddr);
> > + if (!neigh)
> > + goto tx_err_link_failure;
> >
> > - if (addr_type == IPV6_ADDR_ANY)
> > - addr6 = &ipv6_hdr(skb)->daddr;
> > + addr6 = (struct in6_addr *)&neigh->primary_key;
> > + addr_type = ipv6_addr_type(addr6);
> >
> > - memcpy(&fl6->daddr, addr6, sizeof(fl6->daddr));
> > - neigh_release(neigh);
> > - }
> > - } else if (t->parms.proto != 0 && !(t->parms.flags &
> > - (IP6_TNL_F_USE_ORIG_TCLASS |
> > - IP6_TNL_F_USE_ORIG_FWMARK))) {
> > - /* enable the cache only if neither the outer protocol nor the
> > - * routing decision depends on the current inner header value
> > - */
> > - use_cache = true;
> > - }
> > + if (addr_type == IPV6_ADDR_ANY)
> > + addr6 = &ipv6_hdr(skb)->daddr;
> >
> > - if (use_cache)
> > - dst = ip6_tnl_dst_get(t);
> > + memcpy(&fl6->daddr, addr6, sizeof(fl6->daddr));
> > + neigh_release(neigh);
> > + } else if (!fl6->flowi6_mark)
> > + dst = dst_cache_get(&t->dst_cache);
> >
> > if (!ip6_tnl_xmit_ctl(t, &fl6->saddr, &fl6->daddr))
> > goto tx_err_link_failure;
> > @@ -1156,8 +1053,8 @@ static int ip6_tnl_xmit2(struct sk_buff
> > skb = new_skb;
> > }
> >
> > - if (use_cache && ndst)
> > - ip6_tnl_dst_set(t, ndst);
> > + if (!fl6->flowi6_mark && ndst)
> > + dst_cache_set_ip6(&t->dst_cache, ndst, &fl6->saddr);
> > skb_dst_set(skb, dst);
> >
> > skb->transport_header = skb->network_header;
>
> This part looks essentially like a revert of earlier commit befb92542439
> ("ipv6: check skb->protocol before lookup for nexthop", mainline
> 199ab00f3cdb). Is it possible that it comes from an incorrect resolution
> of the conflict caused by these two being backported in opposite order
> (befb92542439 < b8c7f80cbdcd) than the original mainline commits
> (607f725f6f7d < 199ab00f3cdb)?

Hm, I don't really know, it seems to be correct to me...

Manoj, any ideas? You did this backport.

thanks,

greg k-h

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