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

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Date:   Tue, 3 May 2022 14:17:42 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     patchwork-bot+netdevbpf@...nel.org
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        David 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>,
        linux-rdma <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH v2] net: rds: acquire refcount on TCP sockets

On Tue, May 3, 2022 at 4:40 AM <patchwork-bot+netdevbpf@...nel.org> wrote:
>
> Hello:
>
> This patch was applied to netdev/net.git (master)
> by Paolo Abeni <pabeni@...hat.com>:
>
> On Mon, 2 May 2022 10:40:18 +0900 you 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>
> >
> > [...]
>
> Here is the summary with links:
>   - [v2] net: rds: acquire refcount on TCP sockets
>     https://git.kernel.org/netdev/net/c/3a58f13a881e
>
> You are awesome, thank you!
> --
> Deet-doot-dot, I am a bot.
> https://korg.docs.kernel.org/patchwork/pwbot.html
>
>

I think we merged this patch too soon.

My question is : What prevents rds_tcp_conn_path_connect(), and thus
rds_tcp_tune() to be called
after the netns refcount already reached 0 ?

I guess we can wait for next syzbot report, but I think that get_net()
should be replaced
by maybe_get_net()