Re: [PATCH net 3/3] tcp: do not inherit out_of_order_queue from parent

[Hyunwoo Kim <imv4bel@gmail.com>]

On Mon, Aug 17, 2026 at 08:27:32PM +0800, Jiayuan Chen wrote:
> 
> On 8/17/26 5:03 PM, Hyunwoo Kim wrote:
> > A child gets a copy of the parent's out_of_order_queue, which can be non
> > empty when/if parent morphs from listener to active session. Parent and
> > child then point at the same rbtree.
> > 
> > The parent is no longer a listener, so inet_csk_reqsk_queue_add() forgets
> > the child immediately, and tcp_disconnect() frees the skbs the parent
> > still owns. The parent's own root and ooo_last_skb are left alone, so it
> > keeps using those skbs. That is a use-after-free, and the parent frees
> > them a second time when it closes.
> > 
> > We need to make sure this can not happen, by initializing the queue after
> > socket cloning.
> > 
> > Very similar to commit 8b485ce69876 ("tcp: do not inherit fastopen_req
> > from parent")
> > 
> > Fixes: 9f5afeae5152 ("tcp: use an RB tree for ooo receive queue")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
> > ---
> >   net/ipv4/tcp_minisocks.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> > index 6ab3e3a0b43173..d13813d50947dd 100644
> > --- a/net/ipv4/tcp_minisocks.c
> > +++ b/net/ipv4/tcp_minisocks.c
> > @@ -591,6 +591,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
> >   	newtp->total_retrans = req->num_retrans;
> >   	tcp_init_xmit_timers(newsk);
> > +	newtp->out_of_order_queue = RB_ROOT;
> 
> 
> Does tcp_rtx_queue suffer from the same issue?

No, sk_clone() already clears it:

	sock_copy(newsk, sk);
	[...]
	newsk->sk_send_head	= NULL;    // tcp_rtx_queue

I also checked this at runtime, and the child's rtx queue was always
empty even when the parent's was not.


Best regards,
Hyunwoo Kim