Messages in this thread | | | From | Eric Dumazet <> | Date | Wed, 1 Mar 2017 21:36:08 -0800 | Subject | Re: net: use-after-free in neigh_timer_handler/sock_wfree |
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On Wed, Mar 1, 2017 at 9:25 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote: > On Wed, Mar 1, 2017 at 3:15 PM, Eric Dumazet <edumazet@google.com> wrote: >> On Wed, Mar 1, 2017 at 3:09 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote: >> >>> >>> But I doubt skb_orphan() is the solution here, shouldn't we just >>> update sk->sk_wmem_alloc with skb->truesize changes? >> >> Is it worth it ? Apart from syszkaller I mean... >> >> We started with something that had a real impact on real workloads. >> >> 158f323b9868b59967ad96957c4ca388161be321 net: adjust skb->truesize in >> pskb_expand_head() >> >> Note that auditing the stack took me a while. > > I don't know how sk refcnt could work correctly without making > sk_wmem_alloc correctly. We certainly could just call skb_orphan() > is we don't need skb->sk any more, probably like the frag case, > but for this case, the neigh one, the skb's sitting in neigh->arp_queue > are not going to be freed unless in failed case, therefore skb->sk > should not be orphaned so early.
There is absolutely no issue in arp/nd case. Many skbs can sit there and it is fine. Same with skbs sitting a long time in a qdisc.
Of course we try to not call skb_orphan() unless really needed.
tcp_gso_segment() tries very hard to propagate skb ownership to the segments, but even something apparently easy like that took some patches before being done right.
(for details : 0d08c42cf9a71530fef5ebcfe368f38f2dd0476f "tcp: gso: fix truesize tracking")
conntrack reasm is mostly used in forwarding workloads, where skb->sk is already NULL.
Are you thinking of a real workload where skb->sk _needs_ to be kept in ipv6 reasm ?
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