netdev - Re: [PATCH v1 net 2/2] rds: tcp: Fix use-after-free of net in reqsk_timer

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Message-ID: <CANn89iKD9i-UKABN2XVczfYsrSKC81VUVQH+eJxYGgdz42ExTQ@mail.gmail.com>
Date: Fri, 23 Feb 2024 19:09:27 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Allison Henderson <allison.henderson@...cle.com>, 
	Sowmini Varadhan <sowmini.varadhan@...cle.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	linux-rdma@...r.kernel.org, rds-devel@....oracle.com, 
	syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH v1 net 2/2] rds: tcp: Fix use-after-free of net in reqsk_timer_handler().

On Fri, Feb 23, 2024 at 6:26 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> syzkaller reported a warning of netns tracker [0] followed by KASAN
> splat [1] and another ref tracker warning [1].
>
> syzkaller could not find a repro, but in the log, the only suspicious
> sequence was as follows:
>
>   18:26:22 executing program 1:
>   r0 = socket$inet6_mptcp(0xa, 0x1, 0x106)
>   ...
>   connect$inet6(r0, &(0x7f0000000080)={0xa, 0x4001, 0x0, @loopback}, 0x1c) (async)
>
> The notable thing here is 0x4001 in connect(), which is RDS_TCP_PORT.
>
> So, the scenario would be:
>
>   1. unshare(CLONE_NEWNET) creates a per netns tcp listener in
>       rds_tcp_listen_init().
>   2. syz-executor connect()s to it and creates a reqsk.
>   3. syz-executor exit()s immediately.
>   4. netns is dismantled.  [0]
>   5. reqsk timer is fired, and UAF happens while freeing reqsk.  [1]
>   6. listener is freed after RCU grace period.  [2]
>
> Basically, reqsk assumes that the listener guarantees netns safety
> until all reqsk timers are expired by holding the listener's refcount.
> However, this was not the case for kernel sockets.
>
> Commit 740ea3c4a0b2 ("tcp: Clean up kernel listener's reqsk in
> inet_twsk_purge()") fixed this issue only for per-netns ehash, but
> the issue still exists for the global ehash.
>
> We can apply the same fix, but this issue is specific to RDS.
>
> Instead of iterating potentially large ehash and purging reqsk during
> netns dismantle, let's hold netns refcount for the kernel TCP listener.
>
>
> Reported-by: syzkaller <syzkaller@...glegroups.com>
> Fixes: 467fa15356ac ("RDS-TCP: Support multiple RDS-TCP listen endpoints, one per netns.")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
>  net/rds/tcp_listen.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
> index 05008ce5c421..4f7863932df7 100644
> --- a/net/rds/tcp_listen.c
> +++ b/net/rds/tcp_listen.c
> @@ -282,6 +282,11 @@ struct socket *rds_tcp_listen_init(struct net *net, bool isv6)
>                 goto out;
>         }
>
> +       __netns_tracker_free(net, &sock->sk->ns_tracker, false);
> +       sock->sk->sk_net_refcnt = 1;
> +       get_net_track(net, &sock->sk->ns_tracker, GFP_KERNEL);
> +       sock_inuse_add(net, 1);
> +

Why using sock_create_kern() then later 'convert' this kernel socket
to a user one ?

Would using __sock_create() avoid this ?