Fix checksum offset calculation

[flowspec-xdp] / genrules.py

diff --git a/genrules.py b/genrules.py
index 51e547d2d28a12f346aac036cd63f052637b757a..da42e01732795f85a6c30b3e53913d7ac9a304f9 100755 (executable)
--- a/genrules.py
+++ b/genrules.py
@@ -4,6 +4,7 @@ import sys
 import ipaddress
 from enum import Enum
 import argparse
+import math
 
 
 IP_PROTO_ICMP = 1
@@ -288,6 +289,7 @@ with open("rules.h", "w") as out:
     rules4 = ""
     use_v6_frags = False
     rulecnt = 0
+    ratelimitcnt = 0
 
     lastrule = None
     for line in sys.stdin.readlines():
@@ -368,11 +370,59 @@ with open("rules.h", "w") as out:
                     continue
                 ty = blocks[1].strip()[:6]
                 low_bytes = int(blocks[2].strip(") \n"), 16)
-                if ty == "0x8006":
+                if ty == "0x8006" or ty == "0x800c":
+                    if first_action is not None:
+                        # Two ratelimit actions, just drop the old one. RFC 8955 says we can.
+                        first_action = None
+                    exp = (low_bytes & (0xff << 23)) >> 23
                     if low_bytes == 0:
                         first_action = "return XDP_DROP;"
+                    elif low_bytes & (1 <<  31) != 0:
+                        # Negative limit, just drop
+                        first_action = "return XDP_DROP;"
+                    elif exp == 0xff:
+                        # NaN/INF. Just treat as INF and accept
+                        first_action = None
+                    elif exp <= 127: # < 1
+                        first_action = "return XDP_DROP;"
+                    elif exp >= 127 + 63: # The count won't even fit in 64-bits, just accept
+                        first_action = None
                     else:
-                        assert False # Not yet supported
+                        mantissa = low_bytes & ((1 << 23) - 1)
+                        value = 1.0 + mantissa / (2**23)
+                        value *= 2**(exp-127)
+                        if ty == "0x8006":
+                            accessor = "rate->rate.sent_bytes"
+                        else:
+                            accessor = "rate->rate.sent_packets"
+                        # Note that int64_t will overflow after 292 years of uptime
+                        first_action = "int64_t time = bpf_ktime_get_ns();\n"
+                        first_action += f"const uint32_t ratelimitidx = {ratelimitcnt};\n"
+                        first_action +=  "uint64_t allowed_since_last = 0;\n"
+                        first_action +=  "struct ratelimit *rate = bpf_map_lookup_elem(&rate_map, &ratelimitidx);\n"
+                        first_action +=  "if (rate) {\n"
+                        first_action +=  "\tbpf_spin_lock(&rate->lock);\n"
+                        first_action += f"\tif (likely({accessor} > 0))" + " {\n"
+                        first_action +=  "\t\tint64_t diff = time - rate->sent_time;\n"
+                        # Unlikely or not, if the flow is slow, take a perf hit (though with the else if branch it doesn't matter)
+                        first_action +=  "\t\tif (unlikely(diff > 1000000000))\n"
+                        first_action += f"\t\t\t{accessor} = 0;\n"
+                        first_action +=  "\t\telse if (likely(diff > 0))\n"
+                        first_action += f"\t\t\tallowed_since_last = ((uint64_t)diff) * {math.floor(value)} / 1000000000;\n"
+                        first_action +=  "\t}\n"
+                        first_action += f"\tif ({accessor} - ((int64_t)allowed_since_last) <= 0)" + " {\n"
+                        if ty == "0x8006":
+                            first_action += f"\t\t{accessor} = data_end - pktdata;\n"
+                        else:
+                            first_action += f"\t\t{accessor} = 1;\n"
+                        first_action +=  "\t\trate->sent_time = time;\n"
+                        first_action +=  "\t\tbpf_spin_unlock(&rate->lock);\n"
+                        first_action +=  "\t} else {\n"
+                        first_action +=  "\t\tbpf_spin_unlock(&rate->lock);\n"
+                        first_action +=  "\t\treturn XDP_DROP;\n"
+                        first_action +=  "\t}\n"
+                        first_action +=  "}\n"
+                        ratelimitcnt += 1
                 elif ty == "0x8007":
                     if low_bytes & 1 == 0:
                         last_action = "return XDP_PASS;"
@@ -389,7 +439,8 @@ with open("rules.h", "w") as out:
                         write_rule("uint8_t orig_tos = ip->tos;")
                         write_rule("ip->tos = (ip->tos & 3) | " + str(low_bytes << 2) + ";")
                         write_rule("chk = (chk - orig_tos + ip->tos);")
-                        write_rule("if (unlikely(chk < 0)) { chk += 65534; }")
+                        write_rule("if (unlikely(chk > 0xffff)) { chk -= 65535; }")
+                        write_rule("else if (unlikely(chk < 0)) { chk += 65535; }")
                         write_rule("ip->check = ~BE16(chk);")
                     else:
                         write_rule("ip6->priority = " + str(low_bytes >> 2) + ";")
@@ -407,6 +458,8 @@ with open("rules.h", "w") as out:
 
     out.write("\n")
     out.write(f"#define RULECNT {rulecnt}\n")
+    if ratelimitcnt != 0:
+        out.write(f"#define RATE_CNT {ratelimitcnt}\n")
     if rules4 != "":
         out.write("#define NEED_V4_PARSE\n")
         out.write("#define RULES4 {\\\n" + rules4 + "}\n")