On Thu, Apr 11, 2019 at 5:09 PM Daniel Borkmann daniel@iogearbox.net wrote:
On 04/09/2019 04:06 PM, Alan Maguire wrote:
commit 868d523535c2 ("bpf: add bpf_skb_adjust_room encap flags") introduced support to bpf_skb_adjust_room for GSO-friendly GRE and UDP encapsulation.
For GSO to work for skbs, the inner headers (mac and network) need to be marked. For L3 encapsulation using bpf_skb_adjust_room, the mac and network headers are identical. Here we provide a way of specifying the inner mac header length for cases where L2 encap is desired. Such an approach can support encapsulated ethernet headers, MPLS headers etc. For example to convert from a packet of form [eth][ip][tcp] to [eth][ip][udp][inner mac][ip][tcp], something like the following could be done:
headroom = sizeof(iph) + sizeof(struct udphdr) + inner_maclen; ret = bpf_skb_adjust_room(skb, headroom, BPF_ADJ_ROOM_MAC, BPF_F_ADJ_ROOM_ENCAP_L4_UDP | BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 | BPF_F_ADJ_ROOM_ENCAP_L2(inner_maclen));Signed-off-by: Alan Maguire alan.maguire@oracle.com
include/uapi/linux/bpf.h | 10 ++++++++++ net/core/filter.c | 12 ++++++++---- 2 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 8370245..912391c 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1500,6 +1500,10 @@ struct bpf_stack_build_id {
* **BPF_F_ADJ_ROOM_ENCAP_L4_UDP **:Use with ENCAP_L3 flags to further specify the tunnel type.
* **BPF_F_ADJ_ROOM_ENCAP_L2(len) **:
Use with ENCAP_L3/L4 flags to further specify the tunnel
type; **len** is the length of the inner MAC header.
A call to this helper is susceptible to change the underlayingpacket buffer. Therefore, at load time, all checks on pointerspreviously done by the verifier are invalidated and must be@@ -2641,10 +2645,16 @@ enum bpf_func_id { /* BPF_FUNC_skb_adjust_room flags. */ #define BPF_F_ADJ_ROOM_FIXED_GSO (1ULL << 0)
+#define BPF_ADJ_ROOM_ENCAP_L2_MASK 0xff +#define BPF_ADJ_ROOM_ENCAP_L2_SHIFT 56
Would appreciate a small whitespace cleanup in that tab after the define is replaced with a normal space like in the rest of the file.
#define BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 (1ULL << 1) #define BPF_F_ADJ_ROOM_ENCAP_L3_IPV6 (1ULL << 2) #define BPF_F_ADJ_ROOM_ENCAP_L4_GRE (1ULL << 3) #define BPF_F_ADJ_ROOM_ENCAP_L4_UDP (1ULL << 4) +#define BPF_F_ADJ_ROOM_ENCAP_L2(len) (((__u64)len & \
BPF_ADJ_ROOM_ENCAP_L2_MASK) \<< BPF_ADJ_ROOM_ENCAP_L2_SHIFT)Ditto here.
/* Mode for BPF_FUNC_skb_adjust_room helper. */ enum bpf_adj_room_mode { diff --git a/net/core/filter.c b/net/core/filter.c index 22eb2ed..a1654ef62 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2969,11 +2969,14 @@ static u32 bpf_skb_net_base_len(const struct sk_buff *skb) #define BPF_F_ADJ_ROOM_MASK (BPF_F_ADJ_ROOM_FIXED_GSO | \ BPF_F_ADJ_ROOM_ENCAP_L3_MASK | \ BPF_F_ADJ_ROOM_ENCAP_L4_GRE | \
BPF_F_ADJ_ROOM_ENCAP_L4_UDP)
BPF_F_ADJ_ROOM_ENCAP_L4_UDP | \BPF_F_ADJ_ROOM_ENCAP_L2( \BPF_ADJ_ROOM_ENCAP_L2_MASK))static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff, u64 flags) {
One thing that it seems missing in this but also in Willem's earlier set is that we reject these flags in bpf_skb_net_shrink(). Both are called from bpf_skb_adjust_room(), so if we don't support decap yet we should reject such flags so we can extend in future. Could you or Willem send a follow-up?
Indeed. Thanks for bringing that up, Daniel. I only thought of that after submitting the original patchset, too. Will send a patch.