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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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