RE: [PATCH bpf-next V5 4/5] bpf: drop MTU check when doing TC-BPF redirect to ingress
From: John Fastabend <john.fastabend@gmail.com>
Date: 2020-10-30 20:36:30
Also in:
bpf
Jesper Dangaard Brouer wrote:
quoted hunk ↗ jump to hunk
The use-case for dropping the MTU check when TC-BPF does redirect to ingress, is described by Eyal Birger in email[0]. The summary is the ability to increase packet size (e.g. with IPv6 headers for NAT64) and ingress redirect packet and let normal netstack fragment packet as needed. [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/ (local) V4: - Keep net_device "up" (IFF_UP) check. - Adjustment to handle bpf_redirect_peer() helper Signed-off-by: Jesper Dangaard Brouer <redacted> --- include/linux/netdevice.h | 31 +++++++++++++++++++++++++++++-- net/core/dev.c | 19 ++----------------- net/core/filter.c | 14 +++++++++++--- 3 files changed, 42 insertions(+), 22 deletions(-)diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 964b494b0e8d..bd02ddab8dfe 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h@@ -3891,11 +3891,38 @@ int dev_forward_skb(struct net_device *dev, struct sk_buff *skb); bool is_skb_forwardable(const struct net_device *dev, const struct sk_buff *skb); +static __always_inline bool __is_skb_forwardable(const struct net_device *dev, + const struct sk_buff *skb, + const bool check_mtu)
It looks like if check_mtu=false then this is just an interface up check. Can we leave is_skb_forwardable logic alone and just change the spots where this is called with false to something with a name that describes the check, such as is_dev_up(dev). I think it will make this change smaller and the code easier to read. Did I miss something?
+{
+ const u32 vlan_hdr_len = 4; /* VLAN_HLEN */
+ unsigned int len;
+
+ if (!(dev->flags & IFF_UP))
+ return false;
+
+ if (!check_mtu)
+ return true;
+
+ len = dev->mtu + dev->hard_header_len + vlan_hdr_len;
+ if (skb->len <= len)
+ return true;
+
+ /* if TSO is enabled, we don't care about the length as the packet
+ * could be forwarded without being segmented before
+ */
+ if (skb_is_gso(skb))
+ return true;
+
+ return false;
+}
+
static __always_inline int ____dev_forward_skb(struct net_device *dev,
- struct sk_buff *skb)
+ struct sk_buff *skb,
+ const bool check_mtu)
{I guess you will get some duplication here if you have a dev_forward_skb() and a dev_forward_skb_nocheck() or something. Take it or leave it. I know I've added my share of bool swivel bits like this, but better to avoid it if possible IMO. Other than style aspects it looks correct to me.
quoted hunk ↗ jump to hunk
if (skb_orphan_frags(skb, GFP_ATOMIC) || - unlikely(!is_skb_forwardable(dev, skb))) { + unlikely(!__is_skb_forwardable(dev, skb, check_mtu))) { atomic_long_inc(&dev->rx_dropped); kfree_skb(skb); return NET_RX_DROP;diff --git a/net/core/dev.c b/net/core/dev.c index 9499a414d67e..445ccf92c149 100644 --- a/net/core/dev.c +++ b/net/core/dev.c@@ -2188,28 +2188,13 @@ static inline void net_timestamp_set(struct sk_buff *skb)