netdev - Re: [Patch net] tipc: fix the skb_unshare() in tipc_buf

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Date:   Fri, 9 Oct 2020 18:26:31 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     netdev@...r.kernel.org,
        syzbot+e96a7ba46281824cc46a@...kaller.appspotmail.com,
        Xin Long <lucien.xin@...il.com>, Jon Maloy <jmaloy@...hat.com>,
        Ying Xue <ying.xue@...driver.com>
Subject: Re: [Patch net] tipc: fix the skb_unshare() in tipc_buf_append()

On Wed,  7 Oct 2020 21:12:50 -0700 Cong Wang wrote:
> skb_unshare() drops a reference count on the old skb unconditionally,
> so in the failure case, we end up freeing the skb twice here.
> And because the skb is allocated in fclone and cloned by caller
> tipc_msg_reassemble(), the consequence is actually freeing the
> original skb too, thus triggered the UAF by syzbot.
> 
> Fix this by replacing this skb_unshare() with skb_cloned()+skb_copy().
> 
> Fixes: ff48b6222e65 ("tipc: use skb_unshare() instead in tipc_buf_append()")
> Reported-and-tested-by: syzbot+e96a7ba46281824cc46a@...kaller.appspotmail.com
> Cc: Xin Long <lucien.xin@...il.com>
> Cc: Jon Maloy <jmaloy@...hat.com>
> Cc: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

Applied and queued for stable, thank you!