Re: [PATCH v1 net] dccp/tcp: Reset saddr on failure after inet6?_hash_connect().

On Thu, Nov 3, 2022 at 10:24 AM Kuniyuki Iwashima <[email protected]> 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
5d756bbd1f8b5c8f09
> [1]: https://lore.kernel.org/netdev/[email protected]/
>
> Fixes: 3df80d9320bc ("[DCCP]: Introduce DCCPv6")
> Fixes: 7c657876b63c ("[DCCP]: Initial implementation")
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Kuniyuki Iwashima <[email protected]>
> ---
>  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 */