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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. since2c26d34bbc
("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! Fixes:3896d655f4
("bpf: introduce bpf_clone_redirect() helper") Fixes:27b29f6305
("bpf: add bpf_redirect() helper") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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2 changed files with 30 additions and 4 deletions
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@ -2805,6 +2805,23 @@ static inline void skb_postpull_rcsum(struct sk_buff *skb,
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unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
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static inline void skb_postpush_rcsum(struct sk_buff *skb,
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const void *start, unsigned int len)
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{
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/* For performing the reverse operation to skb_postpull_rcsum(),
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* we can instead of ...
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*
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* skb->csum = csum_add(skb->csum, csum_partial(start, len, 0));
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*
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* ... just use this equivalent version here to save a few
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* instructions. Feeding csum of 0 in csum_partial() and later
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* on adding skb->csum is equivalent to feed skb->csum in the
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* first place.
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*/
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if (skb->ip_summed == CHECKSUM_COMPLETE)
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skb->csum = csum_partial(start, len, skb->csum);
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}
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/**
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* pskb_trim_rcsum - trim received skb and update checksum
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* @skb: buffer to trim
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@ -1368,8 +1368,9 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
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/* skb_store_bits cannot return -EFAULT here */
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skb_store_bits(skb, offset, ptr, len);
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if (BPF_RECOMPUTE_CSUM(flags) && skb->ip_summed == CHECKSUM_COMPLETE)
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skb->csum = csum_add(skb->csum, csum_partial(ptr, len, 0));
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if (BPF_RECOMPUTE_CSUM(flags))
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skb_postpush_rcsum(skb, ptr, len);
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return 0;
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}
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@ -1525,8 +1526,12 @@ static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
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if (unlikely(!skb2))
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return -ENOMEM;
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if (BPF_IS_REDIRECT_INGRESS(flags))
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if (BPF_IS_REDIRECT_INGRESS(flags)) {
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if (skb_at_tc_ingress(skb2))
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skb_postpush_rcsum(skb2, skb_mac_header(skb2),
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skb2->mac_len);
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return dev_forward_skb(dev, skb2);
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}
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skb2->dev = dev;
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skb_sender_cpu_clear(skb2);
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@ -1569,8 +1574,12 @@ int skb_do_redirect(struct sk_buff *skb)
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return -EINVAL;
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}
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if (BPF_IS_REDIRECT_INGRESS(ri->flags))
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if (BPF_IS_REDIRECT_INGRESS(ri->flags)) {
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if (skb_at_tc_ingress(skb))
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skb_postpush_rcsum(skb, skb_mac_header(skb),
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skb->mac_len);
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return dev_forward_skb(dev, skb);
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}
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skb->dev = dev;
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skb_sender_cpu_clear(skb);
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