Commit fa7b83bf authored by Dongseok Yi's avatar Dongseok Yi Committed by Daniel Borkmann
Browse files

bpf: Check for BPF_F_ADJ_ROOM_FIXED_GSO when bpf_skb_change_proto 



In the forwarding path GRO -> BPF 6 to 4 -> GSO for TCP traffic, the
coalesced packet payload can be > MSS, but < MSS + 20.

bpf_skb_proto_6_to_4() will upgrade the MSS and it can be > the payload
length. After then tcp_gso_segment checks for the payload length if it
is <= MSS. The condition is causing the packet to be dropped.

tcp_gso_segment():
        [...]
        mss = skb_shinfo(skb)->gso_size;
        if (unlikely(skb->len <= mss))
                goto out;
        [...]

Allow to upgrade/downgrade MSS only when BPF_F_ADJ_ROOM_FIXED_GSO is
not set.

Signed-off-by: default avatarDongseok Yi <dseok.yi@samsung.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarWillem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/bpf/1620804453-57566-1-git-send-email-dseok.yi@samsung.com
parent c49661aa

net/core/filter.c

+13 −9
Original line number Diff line number Diff line
@@ -3235,7 +3235,7 @@ static int bpf_skb_net_hdr_pop(struct sk_buff *skb, u32 off, u32 len) 
	return ret;

}



static int bpf_skb_proto_4_to_6(struct sk_buff *skb)

static int bpf_skb_proto_4_to_6(struct sk_buff *skb, u64 flags)

{

	const u32 len_diff = sizeof(struct ipv6hdr) - sizeof(struct iphdr);

	u32 off = skb_mac_header_len(skb);
@@ -3264,7 +3264,9 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb) 
		}



		/* Due to IPv6 header, MSS needs to be downgraded. */

		if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))

			skb_decrease_gso_size(shinfo, len_diff);



		/* Header must be checked, and gso_segs recomputed. */

		shinfo->gso_type |= SKB_GSO_DODGY;

		shinfo->gso_segs = 0;
@@ -3276,7 +3278,7 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb) 
	return 0;

}



static int bpf_skb_proto_6_to_4(struct sk_buff *skb)

static int bpf_skb_proto_6_to_4(struct sk_buff *skb, u64 flags)

{

	const u32 len_diff = sizeof(struct ipv6hdr) - sizeof(struct iphdr);

	u32 off = skb_mac_header_len(skb);
@@ -3305,7 +3307,9 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb) 
		}



		/* Due to IPv4 header, MSS can be upgraded. */

		if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))

			skb_increase_gso_size(shinfo, len_diff);



		/* Header must be checked, and gso_segs recomputed. */

		shinfo->gso_type |= SKB_GSO_DODGY;

		shinfo->gso_segs = 0;
@@ -3317,17 +3321,17 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb) 
	return 0;

}



static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto)

static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto, u64 flags)

{

	__be16 from_proto = skb->protocol;



	if (from_proto == htons(ETH_P_IP) &&

	      to_proto == htons(ETH_P_IPV6))

		return bpf_skb_proto_4_to_6(skb);

		return bpf_skb_proto_4_to_6(skb, flags);



	if (from_proto == htons(ETH_P_IPV6) &&

	      to_proto == htons(ETH_P_IP))

		return bpf_skb_proto_6_to_4(skb);

		return bpf_skb_proto_6_to_4(skb, flags);



	return -ENOTSUPP;

}
@@ -3337,7 +3341,7 @@ BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto, 
{

	int ret;



	if (unlikely(flags))

	if (unlikely(flags & ~(BPF_F_ADJ_ROOM_FIXED_GSO)))

		return -EINVAL;



	/* General idea is that this helper does the basic groundwork
@@ -3357,7 +3361,7 @@ BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto, 
	 * that. For offloads, we mark packet as dodgy, so that headers

	 * need to be verified first.

	 */

	ret = bpf_skb_proto_xlat(skb, proto);

	ret = bpf_skb_proto_xlat(skb, proto, flags);

	bpf_compute_data_pointers(skb);

	return ret;

}