netdev - Re: [PATCH net] tun: fix recovery from gup errors

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Date:	Mon, 24 Jun 2013 11:22:52 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Neil Horman <nhorman@...driver.com>, netdev@...r.kernel.org,
	Brad Hubbard <bhubbard@...hat.com>
Subject: Re: [PATCH net] tun: fix recovery from gup errors

On 06/23/2013 10:19 PM, 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@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>
> I haven't figured out why do we get failures,
> but recovery is clearly wrong.
>
> This is also -stable material.

Acked-by: Jason Wang <jasowang@...hat.com>
>  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;
> +			for (j = 0; j < num_pages; j++)
> +				put_page(page[i + j]);
>  			return -EFAULT;
>  		}
>  		truesize = size * PAGE_SIZE;

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