Re: [PATCH v2 net 1/4] dccp/tcp: Reset saddr on failure after inet6?_hash_connect().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Joanne Koong <joannelkoong@gmail.com>
Date:   Wed, 16 Nov 2022 16:11:21 -0800
> On Wed, Nov 16, 2022 at 2:28 PM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
> >
> > When connect() is called on a socket bound to the wildcard address,
> > we change the socket's saddr to a local address.  If the socket
> > fails to connect() to the destination, we have to reset the saddr.
> >
> > However, when an error occurs after inet_hash6?_connect() in
> > (dccp|tcp)_v[46]_conect(), we forget to reset saddr and leave
> > the socket bound to the address.
> >
> > From the user's point of view, whether saddr is reset or not varies
> > with errno.  Let's fix this inconsistent behaviour.
> >
> > Note that after this patch, the repro [0] will trigger the WARN_ON()
> > in inet_csk_get_port() again, but this patch is not buggy and rather
> > fixes a bug papering over the bhash2's bug for which we need another
> > fix.
> >
> > For the record, the repro causes -EADDRNOTAVAIL in inet_hash6_connect()
> > by this sequence:
> >
> >   s1 = socket()
> >   s1.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
> >   s1.bind(('127.0.0.1', 10000))
> >   s1.sendto(b'hello', MSG_FASTOPEN, (('127.0.0.1', 10000)))
> >   # or s1.connect(('127.0.0.1', 10000))
> >
> >   s2 = socket()
> >   s2.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
> >   s2.bind(('0.0.0.0', 10000))
> >   s2.connect(('127.0.0.1', 10000))  # -EADDRNOTAVAIL
> >
> >   s2.listen(32)  # WARN_ON(inet_csk(sk)->icsk_bind2_hash != tb2);
> >
> > [0]: https://syzkaller.appspot.com/bug?extid=015d756bbd1f8b5c8f09
> >
> > Fixes: 3df80d9320bc ("[DCCP]: Introduce DCCPv6")
> > Fixes: 7c657876b63c ("[DCCP]: Initial implementation")
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> 
> LGTM. Btw, the 4th patch in this series overwrites these changes by
> moving this logic into the new inet_bhash2_reset_saddr() function you
> added, so we could also drop this patch from the series. OTOH, this
> commit message in this patch has some good background context. So I
> don't have a preference either way :)
> 
> Acked-by: Joanne Koong <joannelkoong@gmail.com>

Thanks for reviewing!

Yes, these changes are overwritten later, but only this patch can be
backported to other stable versions, so I kept this separated.


> > ---
> >  net/dccp/ipv4.c     | 2 ++
> >  net/dccp/ipv6.c     | 2 ++
> >  net/ipv4/tcp_ipv4.c | 2 ++
> >  net/ipv6/tcp_ipv6.c | 2 ++
> >  4 files changed, 8 insertions(+)
> >
> > diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
> > index 713b7b8dad7e..40640c26680e 100644
> > --- a/net/dccp/ipv4.c
> > +++ b/net/dccp/ipv4.c
> > @@ -157,6 +157,8 @@ int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> >          * This unhashes the socket and releases the local port, if necessary.
> >          */
> >         dccp_set_state(sk, DCCP_CLOSED);
> > +       if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
> > +               inet_reset_saddr(sk);
> >         ip_rt_put(rt);
> >         sk->sk_route_caps = 0;
> >         inet->inet_dport = 0;
> > diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
> > index e57b43006074..626166cb6d7e 100644
> > --- a/net/dccp/ipv6.c
> > +++ b/net/dccp/ipv6.c
> > @@ -985,6 +985,8 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
> >
> >  late_failure:
> >         dccp_set_state(sk, DCCP_CLOSED);
> > +       if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
> > +               inet_reset_saddr(sk);
> >         __sk_dst_reset(sk);
> >  failure:
> >         inet->inet_dport = 0;
> > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> > index 87d440f47a70..6a3a732b584d 100644
> > --- a/net/ipv4/tcp_ipv4.c
> > +++ b/net/ipv4/tcp_ipv4.c
> > @@ -343,6 +343,8 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> >          * if necessary.
> >          */
> >         tcp_set_state(sk, TCP_CLOSE);
> > +       if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
> > +               inet_reset_saddr(sk);
> >         ip_rt_put(rt);
> >         sk->sk_route_caps = 0;
> >         inet->inet_dport = 0;
> > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> > index 2a3f9296df1e..81b396e5cf79 100644
> > --- a/net/ipv6/tcp_ipv6.c
> > +++ b/net/ipv6/tcp_ipv6.c
> > @@ -359,6 +359,8 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
> >
> >  late_failure:
> >         tcp_set_state(sk, TCP_CLOSE);
> > +       if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
> > +               inet_reset_saddr(sk);
> >  failure:
> >         inet->inet_dport = 0;
> >         sk->sk_route_caps = 0;
> > --
> > 2.30.2