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

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Message-ID: <d3d068eda5ef2d1ab818f01d7d07fab901363446.camel@redhat.com>
Date:   Wed, 04 May 2022 15:09:43 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        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>,
        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, 2022-05-03 at 14:17 -0700, Eric Dumazet wrote:
> 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 fault.


> 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()
> 
Should we revert this patch before the next pull request, if a suitable
incremental fix is not available by then?

It looks like the window of opportunity for the race is roughly the
same?

Thanks!

Paolo