From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Dongseok Yi <dseok.yi@samsung.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Network Development <netdev@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf v2] bpf: check BPF_F_ADJ_ROOM_FIXED_GSO when upgrading mss in 6 to 4
Date: Tue, 11 May 2021 13:42:46 -0400 [thread overview]
Message-ID: <CAF=yD-+8676QHiKD2ZA4e0kVE+11cOi6sa+M-vmx0+05tm1GfQ@mail.gmail.com> (raw)
In-Reply-To: <1620714998-120657-1-git-send-email-dseok.yi@samsung.com>
On Tue, May 11, 2021 at 2:51 AM Dongseok Yi <dseok.yi@samsung.com> wrote:
>
> 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 increase 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 increase MSS when BPF_F_ADJ_ROOM_FIXED_GSO is not set.
>
> Fixes: 6578171a7ff0 (bpf: add bpf_skb_change_proto helper)
> Signed-off-by: Dongseok Yi <dseok.yi@samsung.com>
>
> ---
Thanks. Note that this feature does not preclude the alternatives
discussed, of converting the packet to non-TSO (by clearing gso_size)
or optionally modifying MSS (but that should get okay from TCP
experts).
I would target this for bpf-next and drop the Fixes. But that is
admittedly debatable.
> net/core/filter.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> v2:
> per Willem de Bruijn request,
> checked the flag instead of a generic approach.
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index cae56d0..a98b28d 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3276,7 +3276,7 @@ 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 +3305,8 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb)
> }
>
> /* Due to IPv4 header, MSS can be upgraded. */
> - skb_increase_gso_size(shinfo, len_diff);
> + 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;
> @@ -3317,7 +3318,7 @@ 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;
>
> @@ -3327,7 +3328,7 @@ static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto)
>
> 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 +3338,7 @@ 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;
Once allowing this flag, please immediately support it for both
bpf_skb_proto_6_to_4 and bpf_skb_4_to_6.
We cannot do that later if we ignore the second case now.
> /* General idea is that this helper does the basic groundwork
> @@ -3357,7 +3358,7 @@ 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;
> }
> --
> 2.7.4
>
next prev parent reply other threads:[~2021-05-11 17:43 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20210429102143epcas2p4c8747c09a9de28f003c20389c050394a@epcas2p4.samsung.com>
2021-04-29 10:08 ` [PATCH bpf] bpf: check for data_len before upgrading mss when 6 to 4 Dongseok Yi
2021-05-05 20:55 ` Daniel Borkmann
2021-05-06 0:45 ` Dongseok Yi
2021-05-06 1:45 ` Willem de Bruijn
2021-05-06 2:27 ` Dongseok Yi
2021-05-06 18:21 ` Willem de Bruijn
2021-05-07 0:53 ` Dongseok Yi
2021-05-07 1:25 ` Willem de Bruijn
2021-05-07 1:45 ` Yunsheng Lin
2021-05-07 1:53 ` Willem de Bruijn
2021-05-07 8:25 ` Dongseok Yi
2021-05-07 9:11 ` Yunsheng Lin
2021-05-07 10:36 ` Dongseok Yi
2021-05-07 13:50 ` Willem de Bruijn
2021-05-10 2:22 ` Dongseok Yi
2021-05-10 13:19 ` Willem de Bruijn
2021-05-10 13:46 ` Willem de Bruijn
2021-05-11 1:11 ` Dongseok Yi
2021-05-11 17:38 ` Willem de Bruijn
2021-05-12 0:45 ` Dongseok Yi
[not found] ` <CGME20210511065056epcas2p1788505019deb274f5c57650a2f5d7ef0@epcas2p1.samsung.com>
2021-05-11 6:36 ` [PATCH bpf v2] bpf: check BPF_F_ADJ_ROOM_FIXED_GSO when upgrading mss in " Dongseok Yi
2021-05-11 17:42 ` Willem de Bruijn [this message]
2021-05-12 6:56 ` Dongseok Yi
[not found] ` <CGME20210512074058epcas2p35536c27bdfafaa6431e164c142007f96@epcas2p3.samsung.com>
2021-05-12 7:27 ` [PATCH bpf-next v3] bpf: check for BPF_F_ADJ_ROOM_FIXED_GSO when bpf_skb_change_proto Dongseok Yi
2021-05-12 14:13 ` Willem de Bruijn
2021-05-18 20:10 ` patchwork-bot+netdevbpf
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