Subject: Re: [BUG] acess_ok() missing from zerocopy_sg_from_iovec()

From: Jason Wang <[email-masked]>
Date: Tue, 04 Jun 2013 11:25:40 +0800

On 06/04/2013 09:06 AM, Eric Dumazet wrote:
> On Mon, 2013-06-03 at 17:34 -0700, Eric Dumazet wrote:
>> It looks like access_ok(VERIFY_READ, base, len) checks are missing in
>> drivers/net/tun.c & drivers/net/macvtap.c before the
>> get_user_pages_fast() calls.
>>
>> Or am I missing something ?
>>
> Patch would be :
>
> [PATCH] tun/macvtap: use access_ok(VERIFY_READ)
>
> Zero copy is good if only we make all needed security checks.
>
> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 59e9605..d793b7d 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -522,6 +522,8 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
>  		size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
>  		if (i + size > MAX_SKB_FRAGS)
>  			return -EMSGSIZE;
> +		if (!access_ok(VERIFY_READ, base, len))
> +			return -EFAULT;
>  		num_pages = get_user_pages_fast(base, size, 0, &page[i]);
>  		if (num_pages != size) {
>  			for (i = 0; i < num_pages; i++)
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 89776c5..7a7b3b1 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1008,6 +1008,8 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
>  		size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
>  		if (i + size > MAX_SKB_FRAGS)
>  			return -EMSGSIZE;
> +		if (!access_ok(VERIFY_READ, base, len))
> +			return -EFAULT;
>  		num_pages = get_user_pages_fast(base, size, 0, &page[i]);
>  		if (num_pages != size) {
>  			for (i = 0; i < num_pages; i++)
>
>
> --
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Looks like vhost is the only user of zerocopy now, and it does this
check when virtqueue is initialized in vq_memory_access_ok().