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Add support to record IPv4 encapsulated packets #35

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Add support to record IPv4 encapsulated packets #35

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90f4ba3
Add support to record IPv4 encapsulated packets
Shikugawa Jun 20, 2023
8b0d870
support variable IHL
Shikugawa Jun 22, 2023
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47 changes: 39 additions & 8 deletions pkg/flowctl/data/filter.bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -214,15 +214,14 @@ static inline void record(const struct tcphdr *th, const struct iphdr *ih,
}

static inline int
process_ipv4_tcp(struct __sk_buff *skb)
process_ipv4_tcp(struct __sk_buff *skb, __u64 offset)
{
__u64 data = skb->data;
__u64 data_end = skb->data_end;
__u64 pkt_len = 0;
data += offset;

struct iphdr *ih = (struct iphdr *)(data + sizeof(struct ethhdr));
assert_len(ih, data_end);
pkt_len = data_end - data;

__u8 hdr_len = ih->ihl * 4;
struct tcphdr *th = (struct tcphdr *)((char *)ih + hdr_len);
Expand All @@ -233,19 +232,48 @@ process_ipv4_tcp(struct __sk_buff *skb)
}

static inline int
process_ipv4_icmp(struct __sk_buff *skb)
process_ipv4_icmp(struct __sk_buff *skb, __u64 offset)
{
// bpf_printk("icmp packet");
return TC_ACT_OK;
}

static inline int
process_ipv4_udp(struct __sk_buff *skb)
process_ipv4_udp(struct __sk_buff *skb, __u64 offset)
{
// bpf_printk("udp packet");
return TC_ACT_OK;
}

static inline int
process_ipv4_ipip(struct __sk_buff *skb)
{
__u64 data = skb->data;
__u64 data_end = skb->data_end;
__u64 pkt_len = 0;

struct iphdr *outer_ih = (struct iphdr *)(data + sizeof(struct ethhdr));
assert_len(outer_ih, data_end);
__u64 outer_ih_len = outer_ih->ihl * 4;

struct iphdr *inner_ih = (struct iphdr *)((char *)outer_ih + outer_ih_len);
assert_len(inner_ih, data_end);

if (inner_ih->ihl < 5)
return TC_ACT_SHOT;
Comment on lines +262 to +263
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If the IP header has options, inner_ih->ihl will be greater than 5, right? If you add the IP header (20) length in process_ipv4_tcp, you may need to implement it like the following?

Suggested change
if (inner_ih->ihl < 5)
return TC_ACT_SHOT;
if (inner_ih->ihl != 5)
return TC_ACT_SHOT;

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or you need to calculate correct offset with ih->ihl.

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Actually this tool supports IP option (ihl > 5) but current this PR doesn't calculate offset of inner IP with correct ihl. So let me fix it.


switch (inner_ih->protocol) {
case IPPROTO_ICMP:
return process_ipv4_icmp(skb, outer_ih_len);
case IPPROTO_TCP:
return process_ipv4_tcp(skb, outer_ih_len);
case IPPROTO_UDP:
return process_ipv4_udp(skb, outer_ih_len);
default:
return TC_ACT_OK;
}
}

static inline int
process_ipv4(struct __sk_buff *skb)
{
Expand All @@ -262,11 +290,14 @@ process_ipv4(struct __sk_buff *skb)

switch (ih->protocol) {
case IPPROTO_ICMP:
return process_ipv4_icmp(skb);
return process_ipv4_icmp(skb, 0);
case IPPROTO_TCP:
return process_ipv4_tcp(skb);
return process_ipv4_tcp(skb, 0);
case IPPROTO_UDP:
return process_ipv4_udp(skb);
return process_ipv4_udp(skb, 0);
/* encapsulated packets */
case IPPROTO_IPIP:
return process_ipv4_ipip(skb);
default:
return TC_ACT_OK;
}
Expand Down