From: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Subject: Re: [PATCH net] tun: fix recovery from gup errors
Date: Sun, 23 Jun 2013 19:36:21 +0400
Message-ID: <51C715F5.2050300@cogentembedded.com>
References: <20130623141903.GA21029@redhat.com>
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Cc: linux-kernel@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	Jason Wang <jasowang@redhat.com>,
	Eric Dumazet <edumazet@google.com>,
	Neil Horman <nhorman@tuxdriver.com>, netdev@vger.kernel.org,
	Brad Hubbard <bhubbard@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20130623141903.GA21029@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

Hello.

On 23-06-2013 18:19, Michael S. Tsirkin wrote:

> get user pages might fail partially in tun zero copy
> mode. To recover we need to put all pages that we got,
> but code used a wrong index resulting in double-free
> errors.

> Reported-by: Brad Hubbard <bhubbard@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---

> I haven't figured out why do we get failures,
> but recovery is clearly wrong.

> This is also -stable material.

>   drivers/net/tun.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)

> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index bfa9bb4..c098b1e 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1010,8 +1010,9 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
>   			return -EMSGSIZE;
>   		num_pages = get_user_pages_fast(base, size, 0, &page[i]);
>   		if (num_pages != size) {
> -			for (i = 0; i < num_pages; i++)
> -				put_page(page[i]);
> +			int j;

   Empty line wouldn't hurt here, after declaration.

> +			for (j = 0; j < num_pages; j++)
> +				put_page(page[i + j]);