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Message-ID: <20221118010803.50517-1-kuniyu@amazon.com>
Date: Thu, 17 Nov 2022 17:08:03 -0800
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <joannelkoong@...il.com>
CC: <acme@...driva.com>, <davem@...emloft.net>, <dccp@...r.kernel.org>,
<dsahern@...nel.org>, <edumazet@...gle.com>, <kuba@...nel.org>,
<kuni1840@...il.com>, <kuniyu@...zon.com>, <martin.lau@...nel.org>,
<mathew.j.martineau@...ux.intel.com>, <netdev@...r.kernel.org>,
<pabeni@...hat.com>, <pengfei.xu@...el.com>,
<stephen@...workplumber.org>, <william.xuanziyang@...wei.com>,
<yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH v2 net 3/4] dccp/tcp: Don't update saddr before unlinking sk from the old bucket
From: Joanne Koong <joannelkoong@...il.com>
Date: Thu, 17 Nov 2022 16:55:59 -0800
> On Thu, Nov 17, 2022 at 4:06 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > From: Joanne Koong <joannelkoong@...il.com>
> > Date: Thu, 17 Nov 2022 13:32:18 -0800
> > > On Wed, Nov 16, 2022 at 2:29 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> > > >
> > > > Currently, we update saddr before calling inet_bhash2_update_saddr(), so
> > > > another thread iterating over the bhash2 bucket might see an inconsistent
> >
> > Sorry this should be just bhash ^^^ here.
> >
> > > > address.
> > > >
> > > > Let's update saddr after unlinking sk from the old bhash2 bucket.
> > >
> > > I'm not sure whether this patch is necessary and I'm curious to hear
> > > your thoughts. There's no adverse effect that comes from updating the
> > > sk's saddr before calling inet_bhash2_update_saddr() in the current
> > > code. Another thread can be iterating over the bhash2 bucket, but it
> > > has no effect whether they see this new address or not (eg when they
> > > are iterating through the bucket they are trying to check for bind
> > > conflicts on another socket, and the sk having the new address doesn't
> > > affect this). What are your thoughts?
> >
> > You are right, it seems I was confused.
> >
> > I was thinking that lockless change of saddr could result in data race;
> > another process iterating over bhash might see a corrupted address.
> >
> > So, we need to acquire the bhash lock before updating saddr, and then
> > related code should be in inet_bhash2_update_saddr().
> >
> > But I seem to have forgot to add the lock part... :p
>
> No worries! :) Is acquiring the bhash lock necessary before updating
> saddr? I think the worst case scenario (which would only happen very
> rarely) is that there is another process iterating over bhash, that
> process tries to access the address the exact time the address is
> being updated in this function, causing the other process to see the
> corrupted address, that corrupted address matches that other process's
> socket address, thus causing that other process to reject the bind
> request.
>
> It doesn't seem like that is a big deal, in the rare event where that
> would happen. In my opinion, it's not worth solving for by making the
> common case slower by grabbing the bhash lock.
>
> What are your thoughts?
In that sense, inet_bhash2_update_saddr() is not the common case, I think.
For the IPv4 case, we need not acquire the lock. Adding READ_ONCE()
and WRITE_ONCE() would be enough, but we cannot do so for IPv6 addr.
Also, I think netdev code often fixes such data races reported by
KCSAN.
> > > > Fixes: 28044fc1d495 ("net: Add a bhash2 table hashed by port and address")
> > > > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > > > ---
> > > > include/net/inet_hashtables.h | 2 +-
> > > > net/dccp/ipv4.c | 22 ++++------------------
> > > > net/dccp/ipv6.c | 23 ++++-------------------
> > > > net/ipv4/af_inet.c | 11 +----------
> > > > net/ipv4/inet_hashtables.c | 31 ++++++++++++++++++++++++++++---
> > > > net/ipv4/tcp_ipv4.c | 20 ++++----------------
> > > > net/ipv6/tcp_ipv6.c | 19 +++----------------
> > > > 7 files changed, 45 insertions(+), 83 deletions(-)
> > > >
> > > > diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
> > > > index 3af1e927247d..ba06e8b52264 100644
> > > > --- a/include/net/inet_hashtables.h
> > > > +++ b/include/net/inet_hashtables.h
> > > > @@ -281,7 +281,7 @@ inet_bhash2_addr_any_hashbucket(const struct sock *sk, const struct net *net, in
> > > > * sk_v6_rcv_saddr (ipv6) changes after it has been binded. The socket's
> > > > * rcv_saddr field should already have been updated when this is called.
> > > > */
> > > > -int inet_bhash2_update_saddr(struct inet_bind_hashbucket *prev_saddr, struct sock *sk);
> > > > +int inet_bhash2_update_saddr(struct sock *sk, void *saddr, int family);
> > > >
> > > > void inet_bind_hash(struct sock *sk, struct inet_bind_bucket *tb,
> > > > struct inet_bind2_bucket *tb2, unsigned short port);
> > > > diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
> > > > index 40640c26680e..95e376e3b911 100644
> > > > --- a/net/dccp/ipv4.c
> > > > +++ b/net/dccp/ipv4.c
> > > > @@ -45,11 +45,10 @@ static unsigned int dccp_v4_pernet_id __read_mostly;
> > > > int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > > > {
> > > > const struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
> > > > - struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > > > - __be32 daddr, nexthop, prev_sk_rcv_saddr;
> > > > struct inet_sock *inet = inet_sk(sk);
> > > > struct dccp_sock *dp = dccp_sk(sk);
> > > > __be16 orig_sport, orig_dport;
> > > > + __be32 daddr, nexthop;
> > > > struct flowi4 *fl4;
> > > > struct rtable *rt;
> > > > int err;
> > > > @@ -91,26 +90,13 @@ int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > > > daddr = fl4->daddr;
> > > >
> > > > if (inet->inet_saddr == 0) {
> > > > - if (inet_csk(sk)->icsk_bind2_hash) {
> > > > - prev_addr_hashbucket =
> > > > - inet_bhashfn_portaddr(&dccp_hashinfo, sk,
> > > > - sock_net(sk),
> > > > - inet->inet_num);
> > > > - prev_sk_rcv_saddr = sk->sk_rcv_saddr;
> > > > - }
> > > > - inet->inet_saddr = fl4->saddr;
> > > > - }
> > > > -
> > > > - sk_rcv_saddr_set(sk, inet->inet_saddr);
> > > > -
> > > > - if (prev_addr_hashbucket) {
> > > > - err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > > + err = inet_bhash2_update_saddr(sk, &fl4->saddr, AF_INET);
> > > > if (err) {
> > > > - inet->inet_saddr = 0;
> > > > - sk_rcv_saddr_set(sk, prev_sk_rcv_saddr);
> > > > ip_rt_put(rt);
> > > > return err;
> > > > }
> > > > + } else {
> > > > + sk_rcv_saddr_set(sk, inet->inet_saddr);
> > > > }
> > > >
> > > > inet->inet_dport = usin->sin_port;
> > > > diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
> > > > index 626166cb6d7e..94c101ed57a9 100644
> > > > --- a/net/dccp/ipv6.c
> > > > +++ b/net/dccp/ipv6.c
> > > > @@ -934,26 +934,11 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
> > > > }
> > > >
> > > > if (saddr == NULL) {
> > > > - struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > > > - struct in6_addr prev_v6_rcv_saddr;
> > > > -
> > > > - if (icsk->icsk_bind2_hash) {
> > > > - prev_addr_hashbucket = inet_bhashfn_portaddr(&dccp_hashinfo,
> > > > - sk, sock_net(sk),
> > > > - inet->inet_num);
> > > > - prev_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
> > > > - }
> > > > -
> > > > saddr = &fl6.saddr;
> > > > - sk->sk_v6_rcv_saddr = *saddr;
> > > > -
> > > > - if (prev_addr_hashbucket) {
> > > > - err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > > - if (err) {
> > > > - sk->sk_v6_rcv_saddr = prev_v6_rcv_saddr;
> > > > - goto failure;
> > > > - }
> > > > - }
> > > > +
> > > > + err = inet_bhash2_update_saddr(sk, saddr, AF_INET6);
> > > > + if (err)
> > > > + goto failure;
> > > > }
> > > >
> > > > /* set the source address */
> > > > diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> > > > index 4728087c42a5..0da679411330 100644
> > > > --- a/net/ipv4/af_inet.c
> > > > +++ b/net/ipv4/af_inet.c
> > > > @@ -1230,7 +1230,6 @@ EXPORT_SYMBOL(inet_unregister_protosw);
> > > >
> > > > static int inet_sk_reselect_saddr(struct sock *sk)
> > > > {
> > > > - struct inet_bind_hashbucket *prev_addr_hashbucket;
> > > > struct inet_sock *inet = inet_sk(sk);
> > > > __be32 old_saddr = inet->inet_saddr;
> > > > __be32 daddr = inet->inet_daddr;
> > > > @@ -1260,16 +1259,8 @@ static int inet_sk_reselect_saddr(struct sock *sk)
> > > > return 0;
> > > > }
> > > >
> > > > - prev_addr_hashbucket =
> > > > - inet_bhashfn_portaddr(tcp_or_dccp_get_hashinfo(sk), sk,
> > > > - sock_net(sk), inet->inet_num);
> > > > -
> > > > - inet->inet_saddr = inet->inet_rcv_saddr = new_saddr;
> > > > -
> > > > - err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > > + err = inet_bhash2_update_saddr(sk, &new_saddr, AF_INET);
> > > > if (err) {
> > > > - inet->inet_saddr = old_saddr;
> > > > - inet->inet_rcv_saddr = old_saddr;
> > > > ip_rt_put(rt);
> > > > return err;
> > > > }
> > > > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> > > > index d745f962745e..dcb6bc918966 100644
> > > > --- a/net/ipv4/inet_hashtables.c
> > > > +++ b/net/ipv4/inet_hashtables.c
> > > > @@ -858,7 +858,20 @@ inet_bhash2_addr_any_hashbucket(const struct sock *sk, const struct net *net, in
> > > > return &hinfo->bhash2[hash & (hinfo->bhash_size - 1)];
> > > > }
> > > >
> > > > -int inet_bhash2_update_saddr(struct inet_bind_hashbucket *prev_saddr, struct sock *sk)
> > > > +static void inet_update_saddr(struct sock *sk, void *saddr, int family)
> > > > +{
> > > > +#if IS_ENABLED(CONFIG_IPV6)
> > > > + if (family == AF_INET6) {
> > > > + sk->sk_v6_rcv_saddr = *(struct in6_addr *)saddr;
> > > > + } else
> > > > +#endif
> > > > + {
> > > > + inet_sk(sk)->inet_saddr = *(__be32 *)saddr;
> > > > + sk_rcv_saddr_set(sk, inet_sk(sk)->inet_saddr);
> > > > + }
> > > > +}
> > > > +
> > > > +int inet_bhash2_update_saddr(struct sock *sk, void *saddr, int family)
> > > > {
> > > > struct inet_hashinfo *hinfo = tcp_or_dccp_get_hashinfo(sk);
> > > > struct inet_bind2_bucket *tb2, *new_tb2;
> > > > @@ -867,6 +880,12 @@ int inet_bhash2_update_saddr(struct inet_bind_hashbucket *prev_saddr, struct soc
> > > > int port = inet_sk(sk)->inet_num;
> > > > struct net *net = sock_net(sk);
> > > >
> > > > + if (!inet_csk(sk)->icsk_bind2_hash) {
> > > > + /* Not bind()ed before. */
> > > > + inet_update_saddr(sk, saddr, family);
> > > > + return 0;
> > > > + }
> > > > +
> > > > /* Allocate a bind2 bucket ahead of time to avoid permanently putting
> > > > * the bhash2 table in an inconsistent state if a new tb2 bucket
> > > > * allocation fails.
> > > > @@ -875,12 +894,18 @@ int inet_bhash2_update_saddr(struct inet_bind_hashbucket *prev_saddr, struct soc
> > > > if (!new_tb2)
> > > > return -ENOMEM;
> > > >
> > > > + /* Unlink first not to show the wrong address for other threads. */
> > > > head2 = inet_bhashfn_portaddr(hinfo, sk, net, port);
> > > >
> > > > - spin_lock_bh(&prev_saddr->lock);
> > > > + spin_lock_bh(&head2->lock);
> > > > __sk_del_bind2_node(sk);
> > > > inet_bind2_bucket_destroy(hinfo->bind2_bucket_cachep, inet_csk(sk)->icsk_bind2_hash);
> > > > - spin_unlock_bh(&prev_saddr->lock);
> > > > + spin_unlock_bh(&head2->lock);
> > > > +
> > > > + inet_update_saddr(sk, saddr, family);
> > > > +
> > > > + /* Update bhash2 bucket. */
> > > > + head2 = inet_bhashfn_portaddr(hinfo, sk, net, port);
> > > >
> > > > spin_lock_bh(&head2->lock);
> > > > tb2 = inet_bind2_bucket_find(head2, net, port, l3mdev, sk);
> > > > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> > > > index 6a3a732b584d..23dd7e9df2d5 100644
> > > > --- a/net/ipv4/tcp_ipv4.c
> > > > +++ b/net/ipv4/tcp_ipv4.c
> > > > @@ -199,15 +199,14 @@ static int tcp_v4_pre_connect(struct sock *sk, struct sockaddr *uaddr,
> > > > /* This will initiate an outgoing connection. */
> > > > int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > > > {
> > > > - struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > > > struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
> > > > struct inet_timewait_death_row *tcp_death_row;
> > > > - __be32 daddr, nexthop, prev_sk_rcv_saddr;
> > > > struct inet_sock *inet = inet_sk(sk);
> > > > struct tcp_sock *tp = tcp_sk(sk);
> > > > struct ip_options_rcu *inet_opt;
> > > > struct net *net = sock_net(sk);
> > > > __be16 orig_sport, orig_dport;
> > > > + __be32 daddr, nexthop;
> > > > struct flowi4 *fl4;
> > > > struct rtable *rt;
> > > > int err;
> > > > @@ -251,24 +250,13 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > > > tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
> > > >
> > > > if (!inet->inet_saddr) {
> > > > - if (inet_csk(sk)->icsk_bind2_hash) {
> > > > - prev_addr_hashbucket = inet_bhashfn_portaddr(tcp_death_row->hashinfo,
> > > > - sk, net, inet->inet_num);
> > > > - prev_sk_rcv_saddr = sk->sk_rcv_saddr;
> > > > - }
> > > > - inet->inet_saddr = fl4->saddr;
> > > > - }
> > > > -
> > > > - sk_rcv_saddr_set(sk, inet->inet_saddr);
> > > > -
> > > > - if (prev_addr_hashbucket) {
> > > > - err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > > + err = inet_bhash2_update_saddr(sk, &fl4->saddr, AF_INET);
> > > > if (err) {
> > > > - inet->inet_saddr = 0;
> > > > - sk_rcv_saddr_set(sk, prev_sk_rcv_saddr);
> > > > ip_rt_put(rt);
> > > > return err;
> > > > }
> > > > + } else {
> > > > + sk_rcv_saddr_set(sk, inet->inet_saddr);
> > > > }
> > > >
> > > > if (tp->rx_opt.ts_recent_stamp && inet->inet_daddr != daddr) {
> > > > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> > > > index 81b396e5cf79..2f3ca3190d26 100644
> > > > --- a/net/ipv6/tcp_ipv6.c
> > > > +++ b/net/ipv6/tcp_ipv6.c
> > > > @@ -292,24 +292,11 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
> > > > tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
> > > >
> > > > if (!saddr) {
> > > > - struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > > > - struct in6_addr prev_v6_rcv_saddr;
> > > > -
> > > > - if (icsk->icsk_bind2_hash) {
> > > > - prev_addr_hashbucket = inet_bhashfn_portaddr(tcp_death_row->hashinfo,
> > > > - sk, net, inet->inet_num);
> > > > - prev_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
> > > > - }
> > > > saddr = &fl6.saddr;
> > > > - sk->sk_v6_rcv_saddr = *saddr;
> > > >
> > > > - if (prev_addr_hashbucket) {
> > > > - err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > > - if (err) {
> > > > - sk->sk_v6_rcv_saddr = prev_v6_rcv_saddr;
> > > > - goto failure;
> > > > - }
> > > > - }
> > > > + err = inet_bhash2_update_saddr(sk, saddr, AF_INET6);
> > > > + if (err)
> > > > + goto failure;
> > > > }
> > > >
> > > > /* set the source address */
> > > > --
> > > > 2.30.2
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