Merge pull request #235 from bobrik/ivan/kfree-skb-port

Add proto and port breakdown to kfree_skb
cloudflare · Jul 21, 2023 · 1f0e5c4 · 1f0e5c4
2 parents 51aa663 + 9617e1d
commit 1f0e5c4
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Showing 2 changed files with 105 additions and 5 deletions.
diff --git a/examples/kfree_skb.bpf.c b/examples/kfree_skb.bpf.c
@@ -1,19 +1,98 @@
 #include <vmlinux.h>
 #include <bpf/bpf_tracing.h>
+#include <bpf/bpf_endian.h>
 #include "maps.bpf.h"
 
+#define ETH_P_IPV6 0x86DD
+#define ETH_P_IP 0x0800
+
+struct kfree_skb_key_t {
+    u16 eth_proto;
+    u16 ip_proto;
+    u16 port;
+    u16 reason;
+};
+
 struct {
     __uint(type, BPF_MAP_TYPE_HASH);
-    __uint(max_entries, 1024);
-    __type(key, u16);
+    __uint(max_entries, 10240);
+    __type(key, struct kfree_skb_key_t);
     __type(value, u64);
 } kfree_skb_total SEC(".maps");
 
-SEC("tp_btf/kfree_skb")
-int BPF_PROG(kfree_skb, struct sk_buff *skb, void *location, enum skb_drop_reason reason)
+SEC("tp_btf/kfree_skb") int BPF_PROG(kfree_skb, struct sk_buff *skb, void *location, enum skb_drop_reason reason)
 {
-    u16 key = reason;
+    struct kfree_skb_key_t key;
+    struct ethhdr eth_hdr;
+    struct iphdr ip_hdr;
+    struct ipv6hdr ipv6_hdr;
+    struct tcphdr tcp_hdr;
+    struct udphdr udp_hdr;
+    u16 ip_proto = 0;
+
+    // Same as skb_mac_header_was_set:
+    // * https://elixir.bootlin.com/linux/v6.5-rc1/source/include/linux/skbuff.h#L2899
+    if (skb->mac_header == (typeof(skb->mac_header)) ~0U) {
+        return 0;
+    }
+
+    if (bpf_probe_read_kernel(&eth_hdr, sizeof(eth_hdr), skb->head + skb->mac_header)) {
+        return 0;
+    }
+
+    key.eth_proto = bpf_ntohs(eth_hdr.h_proto);
+
+    if (!key.eth_proto && !bpf_ntohs(skb->protocol)) {
+        return 0;
+    }
+
+    switch (key.eth_proto) {
+    case ETH_P_IP:
+        if (bpf_probe_read_kernel(&ip_hdr, sizeof(ip_hdr), skb->head + skb->network_header) < 0) {
+            return 0;
+        }
+        ip_proto = ip_hdr.protocol;
+        break;
+    case ETH_P_IPV6:
+        if (bpf_probe_read_kernel(&ipv6_hdr, sizeof(ipv6_hdr), skb->head + skb->network_header) < 0) {
+            return 0;
+        }
+        ip_proto = ipv6_hdr.nexthdr;
+        break;
+    }
+
+    key.ip_proto = ip_proto;
+
+    // Same as skb_transport_header_was_set:
+    // * https://elixir.bootlin.com/linux/v6.5-rc1/source/include/linux/skbuff.h#L2860
+    if (skb->transport_header == (typeof(skb->transport_header)) ~0U) {
+        return 0;
+    }
+
+    // Using key.ip_proto directly is not allowed for some reason:
+    //
+    // ; switch (key.ip_proto) {
+    // 48: (54) w1 &= 65535
+    // R1 32-bit pointer arithmetic prohibited
+    switch (ip_proto) {
+    case IPPROTO_TCP:
+        if (bpf_probe_read_kernel(&tcp_hdr, sizeof(tcp_hdr), skb->head + skb->transport_header) < 0) {
+            return 0;
+        }
+        key.port = bpf_ntohs(tcp_hdr.dest);
+        break;
+    case IPPROTO_UDP:
+        if (bpf_probe_read_kernel(&udp_hdr, sizeof(udp_hdr), skb->head + skb->transport_header) < 0) {
+            return 0;
+        }
+        key.port = bpf_ntohs(udp_hdr.dest);
+        break;
+    }
+
+    key.reason = reason;
+
     increment_map(&kfree_skb_total, &key, 1);
+
     return 0;
 }
 

diff --git a/examples/kfree_skb.yaml b/examples/kfree_skb.yaml
@@ -3,6 +3,27 @@ metrics:
     - name: kfree_skb_total
       help: Number of calls into skb:kfree_skb with a per-reason breakdown
       labels:
+        - name: eth_proto
+          size: 2
+          decoders:
+            - name: uint
+            - name: static_map
+              static_map:
+                2048: ipv4
+                34525: ipv6
+        - name: ip_proto
+          size: 2
+          decoders:
+            - name: uint
+            - name: static_map
+              static_map:
+                1: icmp
+                6: tcp
+                17: udp
+        - name: port
+          size: 2
+          decoders:
+            - name: uint
         - name: reason
           size: 2
           decoders: