linux-kernel - Re: net/irda: use-after-free in ircomm_param

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Message-ID: <CAM_iQpUbCggUxAr6OpLx9CM3Gy2N4+B+2+-cgVs=Dd1z_GdL4A@mail.gmail.com>
Date:	Tue, 26 Jan 2016 10:13:29 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Samuel Ortiz <samuel@...tiz.org>,
	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: net/irda: use-after-free in ircomm_param_request

On Mon, Jan 25, 2016 at 7:59 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> It seems that skb can be freed after skb_put() and spinlock unlock,
> but ircomm_param_request reads skb->len afterwards:
>
> int ircomm_param_request(struct ircomm_tty_cb *self, __u8 pi, int flush)
> {
>     ...
>     skb_put(skb, count);
>     spin_unlock_irqrestore(&self->spinlock, flags);
>     pr_debug("%s(), skb->len=%d\n", __func__ , skb->len);
>

This looks correct to me. We can either get rid of that debugging
print or move it under spinlock.