netdev - Re: linux-next: BUG: KASAN: use-after-free in tun_chr

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Date:   Wed, 16 May 2018 00:40:20 -0700
From:   Andrei Vagin <avagin@...tuozzo.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org
Subject: Re: linux-next: BUG: KASAN: use-after-free in tun_chr_close

On Wed, May 16, 2018 at 03:32:59PM +0800, Jason Wang wrote:
> 
> 
> On 2018年05月16日 15:12, Andrei Vagin wrote:
> > Hi Jason,
> > 
> > I think the problem is in "tun: hold a tun socket during ptr_ring_cleanup".
> > 
> > Pls take a look at the attached patch.
> 
> Yes.
> 
> It looks to me it's not necessary to take extra refcnt during release, we
> can just do the cleanup at __tun_detach().
> 
> Could you help to test the attached patch?

I've run my test on the kernel with this patch. It fixes the problem.
The patch looks correct for me.

Acked-by: Andrei Vagin <avagin@...tuozzo.com>

> 
> Thanks
> 

> From 4b5ad75208e379dcb32abb9ac4790a0446f8558b Mon Sep 17 00:00:00 2001
> From: Jason Wang <jasowang@...hat.com>
> Date: Wed, 16 May 2018 15:26:52 +0800
> Subject: [PATCH] tuntap: fix use after free during release
> 
> After commit b196d88aba8a ("tun: fix use after free for ptr_ring") we
> need clean up tx ring during release(). But unfortunately, it tries to
> do the cleanup after socket were destroyed which will lead another
> use-after-free. Fix this by doing the cleanup before dropping the last
> reference of the socket in __tun_detach().
> 
> Reported-by: Andrei Vagin <avagin@...tuozzo.com>
> Fixes: b196d88aba8a ("tun: fix use after free for ptr_ring")
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/net/tun.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 9fbbb32..d45ac37 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -729,6 +729,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
>  		}
>  		if (tun)
>  			xdp_rxq_info_unreg(&tfile->xdp_rxq);
> +		ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);
>  		sock_put(&tfile->sk);
>  	}
>  }
> @@ -3245,7 +3246,6 @@ static int tun_chr_close(struct inode *inode, struct file *file)
>  	struct tun_file *tfile = file->private_data;
>  
>  	tun_detach(tfile, true);
> -	ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);
>  
>  	return 0;
>  }
> -- 
> 2.7.4
>