Commit 7c68d1a6 authored Jan 18, 2018 by Eric Dumazet Committed by David S. Miller Jan 22, 2018

net: qdisc_pkt_len_init() should be more robust



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 d0c081b4 ("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>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 18b0affa

net/core/dev.c

+15 −4

Original line number	Diff line number	Diff line
		@@ -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
		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,

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