netdev - Re: [PATCH net] ebpf: fix bpf_msg_pull

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Date:   Wed, 29 Aug 2018 17:21:35 -0700
From:   Tushar Dave <tushar.n.dave@...cle.com>
To:     john.fastabend@...il.com, ast@...nel.org, daniel@...earbox.net,
        davem@...emloft.net, netdev@...r.kernel.org
Cc:     sowmini.varadhan@...cle.com
Subject: Re: [PATCH net] ebpf: fix bpf_msg_pull_data



On 08/29/2018 05:07 PM, Tushar Dave wrote:
> While doing some preliminary testing it is found that bpf helper
> bpf_msg_pull_data does not calculate the data and data_end offset
> correctly. Fix it!
> 
> Fixes: 015632bb30da ("bpf: sk_msg program helper bpf_sk_msg_pull_data")
> Signed-off-by: Tushar Dave <tushar.n.dave@...cle.com>
> Acked-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> ---
>   net/core/filter.c | 38 +++++++++++++++++++++++++-------------
>   1 file changed, 25 insertions(+), 13 deletions(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index c25eb36..3eeb3d6 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2285,7 +2285,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>   BPF_CALL_4(bpf_msg_pull_data,
>   	   struct sk_msg_buff *, msg, u32, start, u32, end, u64, flags)
>   {
> -	unsigned int len = 0, offset = 0, copy = 0;
> +	unsigned int len = 0, offset = 0, copy = 0, off = 0;
>   	struct scatterlist *sg = msg->sg_data;
>   	int first_sg, last_sg, i, shift;
>   	unsigned char *p, *to, *from;
> @@ -2299,22 +2299,30 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>   	i = msg->sg_start;
>   	do {
>   		len = sg[i].length;
> -		offset += len;
>   		if (start < offset + len)
>   			break;
> +		offset += len;
>   		i++;
>   		if (i == MAX_SKB_FRAGS)
>   			i = 0;
> -	} while (i != msg->sg_end);
> +	} while (i <= msg->sg_end);
>   
> +	/* return error if start is out of range */
>   	if (unlikely(start >= offset + len))
>   		return -EINVAL;
>   
> -	if (!msg->sg_copy[i] && bytes <= len)
> -		goto out;
> +	/* return error if i is last entry in sglist and end is out of range */
> +	if (msg->sg_copy[i] && end > offset + len)
> +		return -EINVAL;
>   
>   	first_sg = i;
>   
> +	/* if i is not last entry in sg list and end (i.e start + bytes) is
> +	 * within this sg[i] then goto out and calculate data and data_end
> +	 */
> +	if (!msg->sg_copy[i] && end <= offset + len)
> +		goto out;
> +
>   	/* At this point we need to linearize multiple scatterlist
>   	 * elements or a single shared page. Either way we need to
>   	 * copy into a linear buffer exclusively owned by BPF. Then
> @@ -2330,9 +2338,14 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>   		i++;
>   		if (i == MAX_SKB_FRAGS)
>   			i = 0;
> -		if (bytes < copy)
> +		if (end < copy)
>   			break;
> -	} while (i != msg->sg_end);
> +	} while (i <= msg->sg_end);
> +
> +	/* return error if i is last entry in sglist and end is out of range */
> +	if (i > msg->sg_end && end > offset + copy)
> +		return -EINVAL;
> +
>   	last_sg = i;
>   
>   	if (unlikely(copy < end - start))
> @@ -2342,23 +2355,22 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>   	if (unlikely(!page))
>   		return -ENOMEM;
>   	p = page_address(page);
> -	offset = 0;
>   
>   	i = first_sg;
>   	do {
>   		from = sg_virt(&sg[i]);
>   		len = sg[i].length;
> -		to = p + offset;
> +		to = p + off;
>   
>   		memcpy(to, from, len);
> -		offset += len;
> +		off += len;
>   		sg[i].length = 0;
>   		put_page(sg_page(&sg[i]));
>   
>   		i++;
>   		if (i == MAX_SKB_FRAGS)
>   			i = 0;
> -	} while (i != last_sg);
> +	} while (i < last_sg);
>   
>   	sg[first_sg].length = copy;
>   	sg_set_page(&sg[first_sg], page, copy, 0);
> @@ -2380,7 +2392,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>   		else
>   			move_from = i + shift;
>   
> -		if (move_from == msg->sg_end)
> +		if (move_from > msg->sg_end)
>   			break;
>   
>   		sg[i] = sg[move_from];
> @@ -2396,7 +2408,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>   	if (msg->sg_end < 0)
>   		msg->sg_end += MAX_SKB_FRAGS;
>   out:
> -	msg->data = sg_virt(&sg[i]) + start - offset;
> +	msg->data = sg_virt(&sg[first_sg]) + start - offset;
>   	msg->data_end = msg->data + bytes;
>   
>   	return 0;
> 

Please discard this patch. I just noticed that Daniel Borkmann sent 
some similar fixes for bpf_msg_pull_data.


-Tushar