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Message-ID: <20221107011451.35814-1-kuniyu@amazon.com>
Date:   Sun, 6 Nov 2022 17:14:51 -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>,
        <netdev@...r.kernel.org>, <pabeni@...hat.com>,
        <william.xuanziyang@...wei.com>, <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH v1 net] dccp/tcp: Reset saddr on failure after inet6?_hash_connect().

From:   Joanne Koong <joannelkoong@...il.com>
Date:   Sun, 6 Nov 2022 11:18:44 -0800
> On Thu, Nov 3, 2022 at 10:24 AM Kuniyuki Iwashima <kuniyu@...zon.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 with 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 [1] 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
> > [1]: https://lore.kernel.org/netdev/20221029001249.86337-1-kuniyu@amazon.com/
> >
> > Fixes: 3df80d9320bc ("[DCCP]: Introduce DCCPv6")
> > Fixes: 7c657876b63c ("[DCCP]: Initial implementation")
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > ---
> >  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
> >
> 
> inet_reset_saddr() sets both inet_saddr and inet_rcv_saddr to 0, but I
> think there are some edge cases where when dccp/tcp_v4/6_connect() is
> called, inet_saddr is 0 but inet_rcv_saddr is not, which means we'd
> need to reset inet_rcv_saddr to its original value. The example case
> I'm looking at is  __inet_bind() where if the request is to bind to a
> multicast address,
> 
>     inet->inet_rcv_saddr = inet->inet_saddr = addr->sin_addr.s_addr;
>     if (chk_addr_ret == RTN_MULTICAST || chk_addr_ret == RTN_BROADCAST)
>         inet->inet_saddr = 0;  /* Use device */

Thanks for reviewing.

We have to take care of these two error paths.

  * (dccp|tcp)_v[46]_coonnect()
  * __inet_stream_connect()

In __inet_stream_connect(), we call ->disconnect(), which already has the
same logic in this patch.

In your edge case, once (dccp|tcp)_v[46]_coonnect() succeeds, both of
inet->inet_saddr and sk_rcv_saddr are non-zero.  If connect() fails after
that, in ->disconnect(), we cannot know if we should restore sk_rcv_saddr
only.  Also, we don't have the previous address there.

For these reasons, we reset both addresses only if the sk was bound to
INADDR_ANY, which we can detect by the SOCK_BINDADDR_LOCK flag.

As you mentinoed, we can restore sk_rcv_saddr for the edge case in
(dccp|tcp)_v[46]_coonnect() but cannot in __inet_stream_connect().

If we do so, we need another flag for the case and another member to save
the old multicast/broadcast address. (+ where we need rehash for bhash2)

What do you think ?

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