BPF update

Fixes a csum issue on ingress. As mentioned previously, net-next seems just fine imho. Later on, will follow up with couple of replacements like ovs_skb_postpush_rcsum() etc.

Thanks!

v1 -> v2:
- Added patch 1 with helper
- Implemented Hannes' idea to just use csum_partial, thanks!

Daniel Borkmann (2):
net, sched: add skb_at_tc_ingress helper
bpf: add skb_postpush_rcsum and fix dev_forward_skb occasions

 include/linux/skbuff.h    | 17 +++++++++++++++++
 include/net/sch_generic.h |  9 +++++++++
 net/core/filter.c         | 17 +++++++++++++----
 net/sched/cls_bpf.c       |  6 +-----
 4 files changed, 40 insertions(+), 9 deletions(-)

1.9.3

Add a skb_at_tc_ingress() as this will be needed elsewhere as well and can hide the ugly ifdef.

---
 include/net/sch_generic.h | 9 +++++++++
 net/sched/cls_bpf.c       | 6 +-----
 2 files changed, 10 insertions(+), 5 deletions(-)

index b2a8e63..636a362 100644
@@ -407,6 +407,15 @@ bool tcf_destroy(struct tcf_proto *tp, bool force);
 void tcf_destroy_chain(struct tcf_proto __rcu **fl);
 int skb_do_redirect(struct sk_buff *);
 
+static inline bool skb_at_tc_ingress(const struct sk_buff *skb)
+{
+#ifdef CONFIG_NET_CLS_ACT
+	return G_TC_AT(skb->tc_verd) & AT_INGRESS;
+#else
+	return false;
+#endif
+}
+
 /* Reset all TX qdiscs greater then index of a device.  */
 static inline void qdisc_reset_all_tx_gt(struct net_device *dev, unsigned int i)
 {

index 99259f5..8dc8430 100644
@@ -79,12 +79,8 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 			    struct tcf_result *res)
 {
 	struct cls_bpf_head *head = rcu_dereference_bh(tp->root);
+	bool at_ingress = skb_at_tc_ingress(skb);
 	struct cls_bpf_prog *prog;
-#ifdef CONFIG_NET_CLS_ACT
-	bool at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
-#else
-	bool at_ingress = false;
-#endif
 	int ret = -1;
 
 	if (unlikely(!skb_mac_header_was_set(skb)))

1.9.3

Add a small helper skb_postpush_rcsum() and fix up redirect locations that need CHECKSUM_COMPLETE fixups on ingress. dev_forward_skb() expects a proper csum that covers also Ethernet header, f.e. since 2c26d34bbcc0 ("net/core: Handle csum for CHECKSUM_COMPLETE VXLAN forwarding"), we also do skb_postpull_rcsum() after pulling Ethernet header off via eth_type_trans().

When using eBPF in a netns setup f.e. with vxlan in collect metadata mode, I can trigger the following csum issue with an IPv6 setup:

  [  505.144065] dummy1: hw csum failure
  [...]
  [  505.144108] Call Trace:
  [  505.144112]  <IRQ>  [<ffffffff81372f08>] dump_stack+0x44/0x5c
  [  505.144134]  [<ffffffff81607cea>] netdev_rx_csum_fault+0x3a/0x40
  [  505.144142]  [<ffffffff815fee3f>] __skb_checksum_complete+0xcf/0xe0
  [  505.144149]  [<ffffffff816f0902>] nf_ip6_checksum+0xb2/0x120
  [  505.144161]  [<ffffffffa08c0e0e>] icmpv6_error+0x17e/0x328 [nf_conntrack_ipv6]
  [  505.144170]  [<ffffffffa0898eca>] ? ip6t_do_table+0x2fa/0x645 [ip6_tables]
  [  505.144177]  [<ffffffffa08c0725>] ? ipv6_get_l4proto+0x65/0xd0 [nf_conntrack_ipv6]
  [  505.144189]  [<ffffffffa06c9a12>] nf_conntrack_in+0xc2/0x5a0 [nf_conntrack]
  [  505.144196]  [<ffffffffa08c039c>] ipv6_conntrack_in+0x1c/0x20 [nf_conntrack_ipv6]
  [  505.144204]  [<ffffffff8164385d>] nf_iterate+0x5d/0x70
  [  505.144210]  [<ffffffff816438d6>] nf_hook_slow+0x66/0xc0
  [  505.144218]  [<ffffffff816bd302>] ipv6_rcv+0x3f2/0x4f0
  [  505.144225]  [<ffffffff816bca40>] ? ip6_make_skb+0x1b0/0x1b0
  [  505.144232]  [<ffffffff8160b77b>] __netif_receive_skb_core+0x36b/0x9a0
  [  505.144239]  [<ffffffff8160bdc8>] ? __netif_receive_skb+0x18/0x60
  [  505.144245]  [<ffffffff8160bdc8>] __netif_receive_skb+0x18/0x60
  [  505.144252]  [<ffffffff8160ccff>] process_backlog+0x9f/0x140
  [  505.144259]  [<ffffffff8160c4a5>] net_rx_action+0x145/0x320
  [...]

What happens is that on ingress, we push Ethernet header back in, either from cls_bpf or right before skb_do_redirect(), but without updating csum. The "hw csum failure" can be fixed by using the new skb_postpush_rcsum() helper for the dev_forward_skb() case to correct the csum diff again.

Thanks to Hannes Frederic Sowa for the csum_partial() idea!

---
 include/linux/skbuff.h | 17 +++++++++++++++++
 net/core/filter.c      | 17 +++++++++++++----
 2 files changed, 30 insertions(+), 4 deletions(-)

index 6b6bd42..07f9ccd 100644
@@ -2805,6 +2805,23 @@ static inline void skb_postpull_rcsum(struct sk_buff *skb,
 
 unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
 
+static inline void skb_postpush_rcsum(struct sk_buff *skb,
+				      const void *start, unsigned int len)
+{
+	/* For performing the reverse operation to skb_postpull_rcsum(),
+	 * we can instead of ...
+	 *
+	 *   skb->csum = csum_add(skb->csum, csum_partial(start, len, 0));
+	 *
+	 * ... just use this equivalent version here to save a few
+	 * instructions. Feeding csum of 0 in csum_partial() and later
+	 * on adding skb->csum is equivalent to feed skb->csum in the
+	 * first place.
+	 */
+	if (skb->ip_summed == CHECKSUM_COMPLETE)
+		skb->csum = csum_partial(start, len, skb->csum);
+}
+
 /**
  *	pskb_trim_rcsum - trim received skb and update checksum
  *	@skb: buffer to trim

index 35e6fed..0db92b5 100644
@@ -1368,8 +1368,9 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
 		/* skb_store_bits cannot return -EFAULT here */
 		skb_store_bits(skb, offset, ptr, len);
 
-	if (BPF_RECOMPUTE_CSUM(flags) && skb->ip_summed == CHECKSUM_COMPLETE)
-		skb->csum = csum_add(skb->csum, csum_partial(ptr, len, 0));
+	if (BPF_RECOMPUTE_CSUM(flags))
+		skb_postpush_rcsum(skb, ptr, len);
+
 	return 0;
 }
 

@@ -1525,8 +1526,12 @@ static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
 	if (unlikely(!skb2))
 		return -ENOMEM;
 
-	if (BPF_IS_REDIRECT_INGRESS(flags))
+	if (BPF_IS_REDIRECT_INGRESS(flags)) {
+		if (skb_at_tc_ingress(skb2))
+			skb_postpush_rcsum(skb2, skb_mac_header(skb2),
+					   skb2->mac_len);
 		return dev_forward_skb(dev, skb2);
+	}
 
 	skb2->dev = dev;
 	skb_sender_cpu_clear(skb2);

@@ -1569,8 +1574,12 @@ int skb_do_redirect(struct sk_buff *skb)
 		return -EINVAL;
 	}
 
-	if (BPF_IS_REDIRECT_INGRESS(ri->flags))
+	if (BPF_IS_REDIRECT_INGRESS(ri->flags)) {
+		if (skb_at_tc_ingress(skb))
+			skb_postpush_rcsum(skb, skb_mac_header(skb),
+					   skb->mac_len);
 		return dev_forward_skb(dev, skb);
+	}
 
 	skb->dev = dev;
 	skb_sender_cpu_clear(skb);

1.9.3

From: Daniel Borkmann <[email protected]>
Date: Thu, 7 Jan 2016 15:50:21 +0100

Series applied.