Add random padding

bpf/egress.c

@@ -128,12 +128,15 @@ int egress_handler(struct __sk_buff* skb) {
   __u16 payload_len = udp_len - sizeof(*udp);
   __u32 seq = 0, ack_seq = 0, conn_cwnd;
   __u32 random = bpf_get_prandom_u32();
+  __u32 padding;
 
   bpf_spin_lock(&conn->lock);
   if (likely(conn->state == CONN_ESTABLISHED)) {
     seq = conn->seq;
     ack_seq = conn->ack_seq;
-    conn->seq += payload_len + conn->settings.padding;
+    padding =
+      conn->settings.padding == PADDING_RANDOM ? (seq + ack_seq) % 11 : conn->settings.padding;
+    conn->seq += payload_len + padding;
   } else {
     if (conn->state == CONN_IDLE) {
       __u32 cooldown = conn_cooldown(conn);
@@ -176,7 +179,7 @@ int egress_handler(struct __sk_buff* skb) {
   conn_cwnd = conn->cwnd;
   bpf_spin_unlock(&conn->lock);
 
-  size_t reserve_len = TCP_UDP_HEADER_DIFF + conn->settings.padding;
+  size_t reserve_len = TCP_UDP_HEADER_DIFF + padding;
   if (ipv4) {
     __be16 old_len = ipv4->tot_len;
     __be16 new_len = htons(ntohs(old_len) + reserve_len);
@@ -192,7 +195,7 @@ int egress_handler(struct __sk_buff* skb) {
   }
 
   __be32 csum_diff = 0;
-  try_tc(mangle_data(skb, ip_end + sizeof(*udp), &csum_diff, conn->settings.padding));
+  try_tc(mangle_data(skb, ip_end + sizeof(*udp), &csum_diff, padding));
   decl_shot(struct tcphdr, tcp, ip_end, skb);
   update_tcp_header(tcp, payload_len, seq, ack_seq, conn_cwnd);
 

bpf/ingress.c

@@ -307,7 +307,10 @@ int ingress_handler(struct xdp_md* xdp) {
   }
   if (will_drop) return XDP_DROP;
 
-  size_t reserve_len = TCP_UDP_HEADER_DIFF + conn->settings.padding;
+  __u32 padding = conn->settings.padding == PADDING_RANDOM
+                    ? (ntohl(tcp->seq) + ntohl(tcp->ack_seq)) % 11
+                    : conn->settings.padding;
+  size_t reserve_len = TCP_UDP_HEADER_DIFF + padding;
   if (ipv4) {
     __be16 old_len = ipv4->tot_len;
     __be16 new_len = htons(ntohs(old_len) - reserve_len);
@@ -328,8 +331,7 @@ int ingress_handler(struct xdp_md* xdp) {
   __u32 csum = (__u16)~ntohs(tcp->check);
 
   __be32 csum_diff = 0;
-  try_xdp(restore_data(xdp, ip_end + sizeof(*tcp), ip_end + ip_payload_len, &csum_diff,
-                       conn->settings.padding));
+  try_xdp(restore_data(xdp, ip_end + sizeof(*tcp), ip_end + ip_payload_len, &csum_diff, padding));
   decl_drop(struct udphdr, udp, ip_end, xdp);
   csum += u32_fold(ntohl(csum_diff));
 

common/defs.h

@@ -145,6 +145,7 @@ static inline void cleanup_malloc_str(char** ptr) { cleanup_malloc((void*)ptr);
 #define MAX_PACKET_SIZE 10000
 
 #define MAX_PADDING_LEN 16
+#define PADDING_RANDOM (-127)
 
 // Used for reading packet data in bulk
 #define SEGMENT_SIZE 64
@@ -246,7 +247,7 @@ static const struct filter_settings FALLBACK_SETTINGS = {
 static inline void filter_settings_apply(struct filter_settings* local,
                                          const struct filter_settings* global) {
   for (int i = 0; i < sizeof_array(local->array); i++)
-    if (local->array[i] < 0) local->array[i] = global->array[i];
+    if (local->array[i] == -1) local->array[i] = global->array[i];
 }
 
 struct conn_tuple {

src/config.c

@@ -131,7 +131,7 @@ int parse_handshake(char* str, struct filter_handshake* h) {
   int nums[2];
   try(parse_int_seq(str, nums, 2));
   for (int i = 0; i < 2; i++)
-    if (nums[i] >= 0) h->array[i] = nums[i];
+    if (nums[i] != -1) h->array[i] = nums[i];
   return 0;
 }
 
@@ -140,11 +140,29 @@ int parse_keepalive(char* str, struct filter_keepalive* k) {
   int nums[4];
   try(parse_int_seq(str, nums, 4));
   for (int i = 0; i < 4; i++)
-    if (nums[i] >= 0) k->array[i] = nums[i];
+    if (nums[i] != -1) k->array[i] = nums[i];
   return 0;
 }
 
-int parse_padding(const char* str) { return parse_int_non_neg(str, 0, MAX_PADDING_LEN); }
+int parse_padding(const char* str, __s16* padding) {
+  if (strcmp(str, "random") == 0)
+    *padding = PADDING_RANDOM;
+  else
+    *padding = try(parse_int_non_neg(str, 0, MAX_PADDING_LEN));
+  return 0;
+}
+
+static int parse_setting(const char* k, char* v, struct filter_settings* settings) {
+  if (strcmp("handshake", k) == 0)
+    try(parse_handshake(v, &settings->handshake));
+  else if (strcmp("keepalive", k) == 0)
+    try(parse_keepalive(v, &settings->keepalive));
+  else if (strcmp("padding", k) == 0)
+    try(parse_padding(v, &settings->padding));
+  else
+    return 0;
+  return 1;
+}
 
 int parse_filter(char* filter_str, struct filter* filters, struct filter_info* info, int size) {
   int ret;
@@ -201,13 +219,7 @@ int parse_filter(char* filter_str, struct filter* filters, struct filter_info* i
     next_delim = strchr(delim, ',');
     if (next_delim) *next_delim = '\0';
     try(parse_kv(delim, &k, &v));
-    if (strcmp("handshake", k) == 0)
-      try(parse_handshake(v, &info[0].settings.handshake));
-    else if (strcmp("keepalive", k) == 0)
-      try(parse_keepalive(v, &info[0].settings.keepalive));
-    else if (strcmp("padding", k) == 0)
-      info[0].settings.padding = try(parse_padding(v));
-    else
+    if (!try(parse_setting(k, v, &info[0].settings)))
       ret(-EINVAL, _("unsupported option type: '%s'"), k);
     if (!next_delim) break;
   }
@@ -249,12 +261,6 @@ int parse_config_file(FILE* file, struct run_args* args) {
       }
       log_verbosity = parsed;
 
-    } else if (strcmp(k, "handshake") == 0) {
-      try(parse_handshake(v, &args->gsettings.handshake));
-    } else if (strcmp(k, "keepalive") == 0) {
-      try(parse_keepalive(v, &args->gsettings.keepalive));
-    } else if (strcmp(k, "padding") == 0) {
-      args->gsettings.padding = try(parse_padding(v));
     } else if (strcmp(k, "filter") == 0) {
       unsigned int fc = args->filter_count;
       ret = parse_filter(v, &args->filters[fc], &args->info[fc], sizeof_array(args->filters) - fc);
@@ -265,7 +271,8 @@ int parse_config_file(FILE* file, struct run_args* args) {
         return ret;
       else
         args->filter_count += ret;
-    } else {
+
+    } else if (!try(parse_setting(k, v, &args->gsettings))) {
       ret(-EINVAL, _("unknown key '%s'"), k);
     }
   }
@@ -303,11 +310,7 @@ int parse_lock_file(FILE* file, struct lock_content* c) {
       try(parse_int_any(v, &c->whitelist_id));
     else if (strcmp(k, "conns_id") == 0)
       try(parse_int_any(v, &c->conns_id));
-    else if (strcmp(k, "handshake") == 0)
-      try(parse_handshake(v, &c->settings.handshake));
-    else if (strcmp(k, "keepalive") == 0)
-      try(parse_keepalive(v, &c->settings.keepalive));
-    else
+    else if (!try(parse_setting(k, v, &c->settings)))
       ret(-EINVAL, _("unknown key '%s'"), k);
   }
   if (!version_checked) ret(-EINVAL, _("no version found in lock file"));
@@ -324,5 +327,6 @@ int write_lock_file(int fd, const struct lock_content* c) {
   try(dprintf(fd, "handshake=%d:%d\n", c->settings.h.i, c->settings.h.r));
   try(dprintf(fd, "keepalive=%d:%d:%d:%d\n", c->settings.k.t, c->settings.k.i, c->settings.k.r,
               c->settings.k.s));
+  try(dprintf(fd, "padding=%d", c->settings.padding));
   return 0;
 }

src/main.h

@@ -51,7 +51,7 @@ struct lock_content {
 
 int parse_handshake(char* str, struct filter_handshake* h);
 int parse_keepalive(char* str, struct filter_keepalive* k);
-int parse_padding(const char* str);
+int parse_padding(const char* str, __s16* padding);
 int parse_filter(char* filter_str, struct filter* filters, struct filter_info* info, int size);
 int parse_config_file(FILE* file, struct run_args* args);
 int parse_lock_file(FILE* file, struct lock_content* c);

src/run.c

@@ -74,7 +74,7 @@ static inline error_t args_parse_opt(int key, char* arg, struct argp_state* stat
       try(parse_keepalive(arg, &args->gsettings.keepalive));
       break;
     case 'p':
-      args->gsettings.padding = try(parse_padding(arg));
+      try(parse_padding(arg, &args->gsettings.padding));
       break;
     case 'F':
       args->file = arg;

src/show.c

@@ -58,7 +58,10 @@ int show_overview(int whitelist_fd, struct filter_settings* gs, int log_verbosit
   if (LOG_ALLOW_INFO) fprintf(out, "%s%s " RESET, log_prefixes[2][0], log_prefixes[2][1]);
   fprintf(out, _("  %ssettings:%s handshake %d:%d, keepalive %d:%d:%d:%d"), BOLD, RESET, gs->h.i,
           gs->h.r, gs->k.t, gs->k.i, gs->k.r, gs->k.s);
-  if (gs->padding) fprintf(out, _(", padding %d"), gs->padding);
+  if (gs->padding == PADDING_RANDOM)
+    fprintf(out, _(", padding random"));
+  else if (gs->padding)
+    fprintf(out, _(", padding %d"), gs->padding);
   fprintf(out, "\n");
 
   char buf[FILTER_FMT_MAX_LEN];
@@ -88,7 +91,12 @@ int show_overview(int whitelist_fd, struct filter_settings* gs, int log_verbosit
         if (i < 3) fprintf(out, ":");
       }
     }
-    if (a->padding != b->padding) fprintf(out, ",padding=%d", info.settings.padding);
+    if (a->padding != b->padding) {
+      if (info.settings.padding == PADDING_RANDOM)
+        fprintf(out, ",padding=random");
+      else
+        fprintf(out, ",padding=%d", info.settings.padding);
+    }
     if (strlen(info.host) != 0) fprintf(out, _(" %s(resolved from %s)"), RESET GRAY, info.host);
     fprintf(out, RESET "\n");
   }