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Message-ID: <20221012192739.91505-1-kuniyu@amazon.com>
Date: Wed, 12 Oct 2022 12:27:39 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <dsahern@...nel.org>, <kraig@...gle.com>,
<kuba@...nel.org>, <kuni1840@...il.com>, <kuniyu@...zon.com>,
<martin.lau@...nel.org>, <netdev@...r.kernel.org>,
<pabeni@...hat.com>, <willemb@...gle.com>,
<yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH v2 net] udp: Update reuse->has_conns under reuseport_lock.
From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 12 Oct 2022 11:59:43 -0700
> On Wed, Oct 12, 2022 at 11:53 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > When we call connect() for a UDP socket in a reuseport group, we have
> > to update sk->sk_reuseport_cb->has_conns to 1. Otherwise, the kernel
> > could select a unconnected socket wrongly for packets sent to the
> > connected socket.
> >
> > However, the current way to set has_conns is illegal and possible to
> > trigger that problem. reuseport_has_conns() changes has_conns under
> > rcu_read_lock(), which upgrades the RCU reader to the updater. Then,
> > it must do the update under the updater's lock, reuseport_lock, but
> > it doesn't for now.
> >
> > For this reason, there is a race below where we fail to set has_conns
> > resulting in the wrong socket selection. To avoid the race, let's split
> > the reader and updater with proper locking.
> >
> > cpu1 cpu2
> > +----+ +----+
> >
> > __ip[46]_datagram_connect() reuseport_grow()
> > . .
> > |- reuseport_has_conns(sk, true) |- more_reuse = __reuseport_alloc(more_socks_size)
> > | . |
> > | |- rcu_read_lock()
> > | |- reuse = rcu_dereference(sk->sk_reuseport_cb)
> > | |
> > | | | /* reuse->has_conns == 0 here */
> > | | |- more_reuse->has_conns = reuse->has_conns
> > | |- reuse->has_conns = 1 | /* more_reuse->has_conns SHOULD BE 1 HERE */
> > | | |
> > | | |- rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb,
> > | | | more_reuse)
> > | `- rcu_read_unlock() `- kfree_rcu(reuse, rcu)
> > |
> > |- sk->sk_state = TCP_ESTABLISHED
> >
> > Fixes: acdcecc61285 ("udp: correct reuseport selection with connected sockets")
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > ---
> > v2:
> > * Fix build failure for CONFIG_IPV6=m
> > * Drop SO_INCOMING_CPU fix, which will be sent for net-next
> > after the v6.1 merge window
> >
> > v1: https://lore.kernel.org/netdev/20221010174351.11024-1-kuniyu@amazon.com/
> > ---
> > include/net/sock_reuseport.h | 11 +++++------
> > net/core/sock_reuseport.c | 15 +++++++++++++++
> > net/ipv4/datagram.c | 2 +-
> > net/ipv4/udp.c | 2 +-
> > net/ipv6/datagram.c | 2 +-
> > net/ipv6/udp.c | 2 +-
> > 6 files changed, 24 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/net/sock_reuseport.h b/include/net/sock_reuseport.h
> > index 473b0b0fa4ab..efc9085c6892 100644
> > --- a/include/net/sock_reuseport.h
> > +++ b/include/net/sock_reuseport.h
> > @@ -43,21 +43,20 @@ struct sock *reuseport_migrate_sock(struct sock *sk,
> > extern int reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog);
> > extern int reuseport_detach_prog(struct sock *sk);
> >
> > -static inline bool reuseport_has_conns(struct sock *sk, bool set)
> > +static inline bool reuseport_has_conns(struct sock *sk)
> > {
> > struct sock_reuseport *reuse;
> > bool ret = false;
> >
> > rcu_read_lock();
> > reuse = rcu_dereference(sk->sk_reuseport_cb);
> > - if (reuse) {
> > - if (set)
> > - reuse->has_conns = 1;
> > - ret = reuse->has_conns;
> > - }
> > + if (reuse && reuse->has_conns)
> > + ret = true;
> > rcu_read_unlock();
> >
> > return ret;
> > }
> >
> > +void reuseport_has_conns_set(struct sock *sk);
> > +
> > #endif /* _SOCK_REUSEPORT_H */
> > diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
> > index 5daa1fa54249..abb414ed4aa7 100644
> > --- a/net/core/sock_reuseport.c
> > +++ b/net/core/sock_reuseport.c
> > @@ -21,6 +21,21 @@ static DEFINE_IDA(reuseport_ida);
> > static int reuseport_resurrect(struct sock *sk, struct sock_reuseport *old_reuse,
> > struct sock_reuseport *reuse, bool bind_inany);
> >
> > +void reuseport_has_conns_set(struct sock *sk)
> > +{
> > + struct sock_reuseport *reuse;
> > +
> > + if (!rcu_access_pointer(sk->sk_reuseport_cb))
> > + return;
> > +
> > + spin_lock(&reuseport_lock);
> > + reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
> > + lockdep_is_held(&reuseport_lock));
>
> Could @reuse be NULL at this point ?
>
> Previous test was performed without reuseport_lock being held.
Usually, sk_reuseport_cb is changed under lock_sock().
The only exception is reuseport_grow() & TCP reqsk migration case.
1) shutdown() TCP listener, which is moved into the latter part of
reuse->socks[] to migrate reqsk.
2) New listen() overflows reuse->socks[] and call reuseport_grow().
3) reuse->max_socks overflows u16 with the new listener.
4) reuseport_grow() pops the old shutdown()ed listener from the array
and update its sk->sk_reuseport_cb as NULL without lock_sock().
shutdown()ed sk->sk_reuseport_cb can be changed without lock_sock().
But, reuseport_has_conns_set() is called only for UDP and under
lock_sock(), so @reuse never be NULL in this case.
> > + reuse->has_conns = 1;
> > + spin_unlock(&reuseport_lock);
> > +}
> > +EXPORT_SYMBOL(reuseport_has_conns_set);
> > +
> > static int reuseport_sock_index(struct sock *sk,
> > const struct sock_reuseport *reuse,
> > bool closed)
> > diff --git a/net/ipv4/datagram.c b/net/ipv4/datagram.c
> > index 405a8c2aea64..5e66add7befa 100644
> > --- a/net/ipv4/datagram.c
> > +++ b/net/ipv4/datagram.c
> > @@ -70,7 +70,7 @@ int __ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
> > }
> > inet->inet_daddr = fl4->daddr;
> > inet->inet_dport = usin->sin_port;
> > - reuseport_has_conns(sk, true);
> > + reuseport_has_conns_set(sk);
> > sk->sk_state = TCP_ESTABLISHED;
> > sk_set_txhash(sk);
> > inet->inet_id = prandom_u32();
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index d63118ce5900..29228231b058 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -448,7 +448,7 @@ static struct sock *udp4_lib_lookup2(struct net *net,
> > result = lookup_reuseport(net, sk, skb,
> > saddr, sport, daddr, hnum);
> > /* Fall back to scoring if group has connections */
> > - if (result && !reuseport_has_conns(sk, false))
> > + if (result && !reuseport_has_conns(sk))
> > return result;
> >
> > result = result ? : sk;
> > diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
> > index df665d4e8f0f..5ecb56522f9d 100644
> > --- a/net/ipv6/datagram.c
> > +++ b/net/ipv6/datagram.c
> > @@ -256,7 +256,7 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
> > goto out;
> > }
> >
> > - reuseport_has_conns(sk, true);
> > + reuseport_has_conns_set(sk);
> > sk->sk_state = TCP_ESTABLISHED;
> > sk_set_txhash(sk);
> > out:
> > diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> > index 91e795bb9ade..56e4523a3004 100644
> > --- a/net/ipv6/udp.c
> > +++ b/net/ipv6/udp.c
> > @@ -182,7 +182,7 @@ static struct sock *udp6_lib_lookup2(struct net *net,
> > result = lookup_reuseport(net, sk, skb,
> > saddr, sport, daddr, hnum);
> > /* Fall back to scoring if group has connections */
> > - if (result && !reuseport_has_conns(sk, false))
> > + if (result && !reuseport_has_conns(sk))
> > return result;
> >
> > result = result ? : sk;
> > --
> > 2.30.2
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