Re: [PATCH net-next 2/2] datagram, udp: Set local address and rehash socket atomically against lookup

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Dec 05, 2024 at 05:35:52PM +0100, Eric Dumazet wrote:
> On Wed, Dec 4, 2024 at 11:12 PM Stefano Brivio <sbrivio@redhat.com> wrote:
[snip]
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 6a01905d379f..8490408f6009 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -639,18 +639,21 @@ struct sock *__udp4_lib_lookup(const struct net *net, __be32 saddr,
> >                 int sdif, struct udp_table *udptable, struct sk_buff *skb)
> >  {
> >         unsigned short hnum = ntohs(dport);
> > -       struct udp_hslot *hslot2;
> > +       struct udp_hslot *hslot, *hslot2;
> >         struct sock *result, *sk;
> >         unsigned int hash2;
> >
> > +       hslot = udp_hashslot(udptable, net, hnum);
> > +       spin_lock_bh(&hslot->lock);
> 
> This is not acceptable.
> UDP is best effort, packets can be dropped.
> Please fix user application expectations.

The packets aren't merely dropped, they're rejected with an ICMP Port
Unreachable.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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