netdev - Re: [PATCH v1 net] net: Remove WARN_ON_ONCE(sk->sk_forward_alloc) from sk_stream_kill

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Message-ID: <20230208010135.84591-1-kuniyu@amazon.com>
Date:   Tue, 7 Feb 2023 17:01:35 -0800
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <kuniyu@...zon.com>
CC:     <christophpaasch@...oud.com>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <kuni1840@...il.com>,
        <matthieu.baerts@...sares.net>, <netdev@...r.kernel.org>,
        <pabeni@...hat.com>, <syzkaller@...glegroups.com>
Subject: Re: [PATCH v1 net] net: Remove WARN_ON_ONCE(sk->sk_forward_alloc) from sk_stream_kill_queues().

From:   Kuniyuki Iwashima <kuniyu@...zon.com>
Date:   Tue, 7 Feb 2023 16:37:13 -0800
> From:   Eric Dumazet <edumazet@...gle.com>
> Date:   Tue, 7 Feb 2023 20:25:19 +0100
> > On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> > >
> > > In commit b5fc29233d28 ("inet6: Remove inet6_destroy_sock() in
> > > sk->sk_prot->destroy()."), we delay freeing some IPv6 resources
> > > from sk->destroy() to sk->sk_destruct().
> > >
> > > Christoph Paasch reported the commit started triggering
> > > WARN_ON_ONCE(sk->sk_forward_alloc) in sk_stream_kill_queues()
> > > (See [0 - 2]).
> > >
> > > For example, if inet6_sk(sk)->rxopt is not zero by setting
> > > IPV6_RECVPKTINFO or its friends, tcp_v6_do_rcv() clones a skb
> > > and calls skb_set_owner_r(), which charges it to sk.
> > 
> > skb_set_owner_r() in this place seems wrong.
> > This could lead to a negative sk->sk_forward_alloc
> > (because we have not sk_rmem_schedule() it ?)
> > 
> > Do you have a repro ?
> 
> I created a repro and confirmed sk->sk_forward_alloc was always positive.

This was just before sk_stream_kill_queues(), and actually
sk->sk_forward_alloc was able to be negative by the
skb_set_owner_r() as you thought.

I'll fix this, thank you!