netdev - Re: [PATCH RFC v2 net-next] rds-tcp: Take explicit refcounts on struct net

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Date:   Thu, 2 Mar 2017 11:07:04 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH RFC v2 net-next] rds-tcp: Take explicit refcounts on
 struct net

On Tue, Feb 28, 2017 at 5:33 PM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> This is a test patch being supplied for a trial run on syzkaller.
>
> It's incorrect for the rds_connection to piggyback on the
> sock_net() refcount for the netns because this gives rise to
> a chicken-and-egg problem during rds_conn_destroy. Instead explicitly
> take a ref on the net, and hold the netns down till the connection
> tear-down is complete.
>
> Dmitry: I'm not sure whether the other 2 panics around rds_sock
> use-after-free are also around netns teardown and/or directly related
> to this- they may be unrelated bugs, could we please give this one
> a trial run, while watching for the others?


The other 2 does not look like net-related, but you also mailed patch
"Cancel any pending connection attempts before taking down
connection", which looks like it should fix the other 2, right?
I now applied both of your patched on bots. But only happened 1+2
times over the last 2 weeks. So it will require at least a month to
make a weak conclusion that it might have helped. So I would suggest
to either (1) re-review the crash reports, the code and the fix and
commit it if everything looks consistent, or (2) write a stress test
that provokes the bugs as much as possible, add some sleeps into the
kernel code, reproduce the crashes and check that the patches fix
them.




> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> ---
>  net/rds/connection.c |    1 +
>  net/rds/rds.h        |    6 +++---
>  net/rds/tcp.c        |    4 ++--
>  3 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/net/rds/connection.c b/net/rds/connection.c
> index 0e04dcc..1fa75ab 100644
> --- a/net/rds/connection.c
> +++ b/net/rds/connection.c
> @@ -429,6 +429,7 @@ void rds_conn_destroy(struct rds_connection *conn)
>          */
>         rds_cong_remove_conn(conn);
>
> +       put_net(conn->c_net);
>         kmem_cache_free(rds_conn_slab, conn);
>
>         spin_lock_irqsave(&rds_conn_lock, flags);
> diff --git a/net/rds/rds.h b/net/rds/rds.h
> index 07fff73..219628f 100644
> --- a/net/rds/rds.h
> +++ b/net/rds/rds.h
> @@ -147,7 +147,7 @@ struct rds_connection {
>
>         /* Protocol version */
>         unsigned int            c_version;
> -       possible_net_t          c_net;
> +       struct net              *c_net;
>
>         struct list_head        c_map_item;
>         unsigned long           c_map_queued;
> @@ -162,13 +162,13 @@ struct rds_connection {
>  static inline
>  struct net *rds_conn_net(struct rds_connection *conn)
>  {
> -       return read_pnet(&conn->c_net);
> +       return conn->c_net;
>  }
>
>  static inline
>  void rds_conn_net_set(struct rds_connection *conn, struct net *net)
>  {
> -       write_pnet(&conn->c_net, net);
> +       conn->c_net = get_net(net);
>  }
>
>  #define RDS_FLAG_CONG_BITMAP   0x01
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 57bb523..bf4c6a3 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -529,7 +529,7 @@ static void rds_tcp_kill_sock(struct net *net)
>         flush_work(&rtn->rds_tcp_accept_w);
>         spin_lock_irq(&rds_tcp_conn_lock);
>         list_for_each_entry_safe(tc, _tc, &rds_tcp_conn_list, t_tcp_node) {
> -               struct net *c_net = read_pnet(&tc->t_cpath->cp_conn->c_net);
> +               struct net *c_net = tc->t_cpath->cp_conn->c_net;
>
>                 if (net != c_net || !tc->t_sock)
>                         continue;
> @@ -584,7 +584,7 @@ static void rds_tcp_sysctl_reset(struct net *net)
>
>         spin_lock_irq(&rds_tcp_conn_lock);
>         list_for_each_entry_safe(tc, _tc, &rds_tcp_conn_list, t_tcp_node) {
> -               struct net *c_net = read_pnet(&tc->t_cpath->cp_conn->c_net);
> +               struct net *c_net = tc->t_cpath->cp_conn->c_net;
>
>                 if (net != c_net || !tc->t_sock)
>                         continue;
> --
> 1.7.1
>