netdev - Re: [PATCH v2] net: rds: acquire refcount on TCP sockets

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Date:   Mon, 2 May 2022 14:12:34 +0000
From:   Haakon Bugge <haakon.bugge@...cle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
CC:     Eric Dumazet <edumazet@...gle.com>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        syzbot <syzbot+694120e1002c117747ed@...kaller.appspotmail.com>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        OFED mailing list <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH v2] net: rds: acquire refcount on TCP sockets



> On 2 May 2022, at 03:40, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> wrote:
> 
> syzbot is reporting use-after-free read in tcp_retransmit_timer() [1],
> for TCP socket used by RDS is accessing sock_net() without acquiring a
> refcount on net namespace. Since TCP's retransmission can happen after
> a process which created net namespace terminated, we need to explicitly
> acquire a refcount.
> 
> Link: https://syzkaller.appspot.com/bug?extid=694120e1002c117747ed [1]
> Reported-by: syzbot <syzbot+694120e1002c117747ed@...kaller.appspotmail.com>
> Fixes: 26abe14379f8e2fa ("net: Modify sk_alloc to not reference count the netns of kernel sockets.")
> Fixes: 8a68173691f03661 ("net: sk_clone_lock() should only do get_net() if the parent is not a kernel socket")
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Tested-by: syzbot <syzbot+694120e1002c117747ed@...kaller.appspotmail.com>
> ---
> Changes in v2:
>  Add Fixes: tag.
>  Move to inside lock_sock() section.
> 
> I chose 26abe14379f8e2fa and 8a68173691f03661 which went to 4.2 for Fixes: tag,
> for refcount was implicitly taken when 70041088e3b97662 ("RDS: Add TCP transport
> to RDS") was added to 2.6.32.
> 
> net/rds/tcp.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
> 
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 5327d130c4b5..2f638f8b7b1e 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -495,6 +495,14 @@ void rds_tcp_tune(struct socket *sock)
> 
> 	tcp_sock_set_nodelay(sock->sk);
> 	lock_sock(sk);
> +	/* TCP timer functions might access net namespace even after
> +	 * a process which created this net namespace terminated.
> +	 */
> +	if (!sk->sk_net_refcnt) {
> +		sk->sk_net_refcnt = 1;
> +		get_net_track(net, &sk->ns_tracker, GFP_KERNEL);

Don't you need a corresponding put_net_track()?


Thxs, Håkon


> +		sock_inuse_add(net, 1);
> +	}
> 	if (rtn->sndbuf_size > 0) {
> 		sk->sk_sndbuf = rtn->sndbuf_size;
> 		sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
> -- 
> 2.34.1
> 
>