From 7ce01cd3013b7c9f1b257a6033b6d1f67fed5b5c Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 7 Jan 2016 15:50:23 +0100 Subject: [PATCH 223/232] bpf: add skb_postpush_rcsum and fix dev_forward_skb occasions 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] [] dump_stack+0x44/0x5c [ 505.144134] [] netdev_rx_csum_fault+0x3a/0x40 [ 505.144142] [] __skb_checksum_complete+0xcf/0xe0 [ 505.144149] [] nf_ip6_checksum+0xb2/0x120 [ 505.144161] [] icmpv6_error+0x17e/0x328 [nf_conntrack_ipv6] [ 505.144170] [] ? ip6t_do_table+0x2fa/0x645 [ip6_tables] [ 505.144177] [] ? ipv6_get_l4proto+0x65/0xd0 [nf_conntrack_ipv6] [ 505.144189] [] nf_conntrack_in+0xc2/0x5a0 [nf_conntrack] [ 505.144196] [] ipv6_conntrack_in+0x1c/0x20 [nf_conntrack_ipv6] [ 505.144204] [] nf_iterate+0x5d/0x70 [ 505.144210] [] nf_hook_slow+0x66/0xc0 [ 505.144218] [] ipv6_rcv+0x3f2/0x4f0 [ 505.144225] [] ? ip6_make_skb+0x1b0/0x1b0 [ 505.144232] [] __netif_receive_skb_core+0x36b/0x9a0 [ 505.144239] [] ? __netif_receive_skb+0x18/0x60 [ 505.144245] [] __netif_receive_skb+0x18/0x60 [ 505.144252] [] process_backlog+0x9f/0x140 [ 505.144259] [] 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! Fixes: 3896d655f4d4 ("bpf: introduce bpf_clone_redirect() helper") Fixes: 27b29f63058d ("bpf: add bpf_redirect() helper") Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- include/linux/skbuff.h | 17 +++++++++++++++++ net/core/filter.c | 17 +++++++++++++---- 2 files changed, 30 insertions(+), 4 deletions(-) --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2737,6 +2737,23 @@ static inline void skb_postpull_rcsum(st 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 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -1288,8 +1288,9 @@ static u64 bpf_skb_store_bytes(u64 r1, u /* 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; } @@ -1415,8 +1416,12 @@ static u64 bpf_clone_redirect(u64 r1, u6 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); @@ -1459,8 +1464,12 @@ 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);