Re: [PATCH net] net: qdisc_pkt_len_init() should be more robust

[Jason Wang <jasowang@redhat.com>]

On 2018年01月19日 11:59, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> Without proper validation of DODGY packets, we might very well
> feed qdisc_pkt_len_init() with invalid GSO packets.
>
> tcp_hdrlen() might access out-of-bound data, so let's use
> skb_header_pointer() and proper checks.
>
> Whole story is described in commit d0c081b49137 ("flow_dissector:
> properly cap thoff field")
>
> We have the goal of validating DODGY packets earlier in the stack,
> so we might very well revert this fix in the future.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Willem de Bruijn <willemb@google.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Reported-by: syzbot+9da69ebac7dddd804552@syzkaller.appspotmail.com
> ---
>   net/core/dev.c |   19 +++++++++++++++----
>   1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0e0ba36eeac9852b8df5ddd398dbc66ad6c83760..613fb4066be7bedbd3cd59ea9cf6eb7ef3100bd0 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3151,10 +3151,21 @@ static void qdisc_pkt_len_init(struct sk_buff *skb)
>   		hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
>   
>   		/* + transport layer */
> -		if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
> -			hdr_len += tcp_hdrlen(skb);
> -		else
> -			hdr_len += sizeof(struct udphdr);
> +		if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
> +			const struct tcphdr *th;
> +			struct tcphdr _tcphdr;
> +
> +			th = skb_header_pointer(skb, skb_transport_offset(skb),
> +						sizeof(_tcphdr), &_tcphdr);
> +			if (likely(th))
> +				hdr_len += __tcp_hdrlen(th);
> +		} else {
> +			struct udphdr _udphdr;
> +
> +			if (skb_header_pointer(skb, skb_transport_offset(skb),
> +					       sizeof(_udphdr), &_udphdr))
> +				hdr_len += sizeof(struct udphdr);
> +		}
>   
>   		if (shinfo->gso_type & SKB_GSO_DODGY)
>   			gso_segs = DIV_ROUND_UP(skb->len - hdr_len,
>

Acked-by: Jason Wang <jasowang@redhat.com>