Implement HMAC authentication.

Known issues:

  - we create a neighbour entry before the first successful challenge;
  - we compute HMAC for each HMAC TLV rather than just once;
  - we only support sending one HMAC TLV;
  - we don't support key rotation.

Co-authored-by: Clara Do <[email protected]>
Co-authored-by: Weronika Kolodziejak <[email protected]>

Makefile

@@ -11,11 +11,11 @@ LDLIBS = -lrt
 
 SRCS = babeld.c net.c kernel.c util.c interface.c source.c neighbour.c \
        route.c xroute.c message.c resend.c configuration.c local.c \
-       rfc6234/sha224-256.c BLAKE2/ref/blake2s-ref.c
+       hmac.c rfc6234/sha224-256.c BLAKE2/ref/blake2s-ref.c
 
 OBJS = babeld.o net.o kernel.o util.o interface.o source.o neighbour.o \
        route.o xroute.o message.o resend.o configuration.o local.o \
-       rfc6234/sha224-256.o BLAKE2/ref/blake2s-ref.o
+       hmac.o rfc6234/sha224-256.o BLAKE2/ref/blake2s-ref.o
 
 babeld: $(OBJS)
 	$(CC) $(CFLAGS) $(LDFLAGS) -o babeld $(OBJS) $(LDLIBS)

babeld.c

@@ -638,9 +638,10 @@ main(int argc, char **argv)
         }
 
         if(FD_ISSET(protocol_socket, &readfds)) {
+            unsigned char to[16];
             rc = babel_recv(protocol_socket,
                             receive_buffer, receive_buffer_size,
-                            (struct sockaddr*)&sin6, sizeof(sin6));
+                            (struct sockaddr*)&sin6, sizeof(sin6), to);
             if(rc < 0) {
                 if(errno != EAGAIN && errno != EINTR) {
                     perror("recv");
@@ -652,7 +653,7 @@ main(int argc, char **argv)
                         continue;
                     if(ifp->ifindex == sin6.sin6_scope_id) {
                         parse_packet((unsigned char*)&sin6.sin6_addr, ifp,
-                                     receive_buffer, rc);
+                                     receive_buffer, rc, to);
                         VALGRIND_MAKE_MEM_UNDEFINED(receive_buffer,
                                                     receive_buffer_size);
                         break;

configuration.c

@@ -39,6 +39,7 @@ THE SOFTWARE.
 #include "interface.h"
 #include "route.h"
 #include "kernel.h"
+#include "hmac.h"
 #include "configuration.h"
 
 static struct filter *input_filters = NULL;
@@ -321,6 +322,35 @@ get_interface_type(int c, int *type_r, gnc_t gnc, void *closure)
     return c;
 }
 
+static int
+gethex(int c, unsigned char **value_r, int *len_r, gnc_t gnc, void *closure)
+{
+    char *t;
+    unsigned char *value;
+    int len, rc;
+    c = getword(c, &t, gnc, closure);
+    if(c < -1)
+        return c;
+    len = strlen(t);
+    if(len % 2 != 0) {
+        free(t);
+        return -2;
+    }
+    value = malloc(len / 2);
+    if(value == NULL)
+        return -2;
+
+    rc = fromhex(value, t, len);
+    free(t);
+    if(rc < 0) {
+        free(value);
+        return -2;
+    }
+    *value_r = value;
+    *len_r = len / 2;
+    return c;
+}
+
 static void
 free_filter(struct filter *f)
 {
@@ -646,6 +676,17 @@ parse_anonymous_ifconf(int c, gnc_t gnc, void *closure,
             if(c < -1 || penalty <= 0 || penalty > 0xFFFF)
                 goto error;
             if_conf->max_rtt_penalty = penalty;
+        } else if(strcmp(token, "hmac") == 0) {
+            char *key_id;
+            struct key *key;
+            c = getword(c, &key_id, gnc, closure);
+            if(c < -1) {
+                free(key_id);
+                goto error;
+            }
+            key = find_key(key_id);
+            if_conf->key = key;
+            free(key_id);
         } else {
             goto error;
         }
@@ -693,6 +734,65 @@ parse_ifconf(int c, gnc_t gnc, void *closure,
     return -2;
 }
 
+static int
+parse_key(int c, gnc_t gnc, void *closure, struct key **key_return)
+{
+    char *token = NULL;
+    struct key *key;
+
+    key = calloc(1, sizeof(struct key));
+    if(key == NULL)
+        goto error;
+    while(1) {
+        c = skip_whitespace(c, gnc, closure);
+        if(c < 0 || c == '\n' || c == '#') {
+            c = skip_to_eol(c, gnc, closure);
+            break;
+        }
+        c = getword(c, &token, gnc, closure);
+        if(c < -1) {
+            goto error;
+        }
+        if(strcmp(token, "id") == 0) {
+            c = getword(c, &key->id, gnc, closure);
+            if(c < -1 || key->id == NULL) {
+                goto error;
+            }
+        } else if(strcmp(token, "type") == 0) {
+            char *auth_type;
+            c = getword(c, &auth_type, gnc, closure);
+            if(c < -1 || auth_type == NULL)
+                goto error;
+            if(strcmp(auth_type, "none") == 0) {
+                key->type = AUTH_TYPE_NONE;
+            } else if(strcmp(auth_type, "sha256") == 0) {
+                key->type = AUTH_TYPE_SHA256;
+            } else if(strcmp(auth_type, "blake2s") == 0) {
+                key->type = AUTH_TYPE_BLAKE2S;
+            } else {
+                key->type = 0;
+                free(auth_type);
+                goto error;
+            }
+            free(auth_type);
+        } else if(strcmp(token, "value") == 0) {
+            c = gethex(c, &key->value, &key->len, gnc, closure);
+            if(c < -1 || key->value == NULL)
+                goto error;
+        } else {
+            goto error;
+        }
+        free(token);
+    }
+    *key_return = key;
+    return c;
+
+ error:
+    free(token);
+    free(key);
+    return -2;
+}
+
 static void
 add_filter(struct filter *filter, struct filter **filters)
 {
@@ -738,6 +838,7 @@ merge_ifconf(struct interface_conf *dest,
     MERGE(rtt_min);
     MERGE(rtt_max);
     MERGE(max_rtt_penalty);
+    MERGE(key);
 
 #undef MERGE
 }
@@ -1093,6 +1194,32 @@ parse_config_line(int c, gnc_t gnc, void *closure,
         if(c < -1 || !action_return)
             goto fail;
         reopen_logfile();
+    } else if(strcmp(token, "key") == 0) {
+        struct key *key = NULL;
+        c = parse_key(c, gnc, closure, &key);
+        if(c < -1)
+            goto fail;
+        if(key->id == NULL)
+            goto fail;
+        switch(key->type) {
+        case AUTH_TYPE_SHA256:
+            if(key->len != 32) {
+                free(key);
+                goto fail;
+            }
+            break;
+        case AUTH_TYPE_BLAKE2S:
+            if(key->len != 16) {
+                free(key);
+                goto fail;
+            }
+            break;
+        default:
+            free(key);
+            goto fail;
+        }
+        add_key(key->id, key->type, key->len, key->value);
+        free(key);
     } else {
         c = parse_option(c, gnc, closure, token);
         if(c < -1)

configuration.h

@@ -29,6 +29,10 @@ THE SOFTWARE.
 #define CONFIG_ACTION_UNMONITOR 4
 #define CONFIG_ACTION_NO 5
 
+#define AUTH_TYPE_NONE 0
+#define AUTH_TYPE_SHA256 1
+#define AUTH_TYPE_BLAKE2S 2
+
 struct filter_result {
     unsigned int add_metric; /* allow = 0, deny = INF, metric = <0..INF> */
     unsigned char *src_prefix;