Support "hidden" UNIX socket path

doc/libnetconf.doc

@@ -304,8 +304,8 @@
  * - ::nc_server_set_capab_withdefaults()
  * - ::nc_server_set_capability()
  * - ::nc_server_endpt_count()
- * - ::nc_server_add_endpt_unix_socket_listen()
- * - ::nc_server_del_endpt_unix_socket()
+ * - ::nc_server_set_unix_socket_path()
+ * - ::nc_server_get_unix_socket_path()
  *
  * Server Configuration
  * ===
@@ -383,7 +383,7 @@
  * You may create this data yourself or by using ::nc_server_config_add_ssh_hostkey().
  *
  * It is important to decide whether the users that can connect to the SSH server should be obtained from the configuration or from the system.
- * If the YANG feature *local-users-supported* is enabled (the default), then the authorized users are derived from the configuration. 
+ * If the YANG feature *local-users-supported* is enabled (the default), then the authorized users are derived from the configuration.
  * When a client connects to the server, he must be found in the configuration and he must authenticate to **all** of his configured authentication methods.
  * If the feature is disabled, then the system will be used to try to authenticate the client via one of the three
  * methods - publickey, keyboard-interactive or password (only one of them has to succeed).
@@ -493,6 +493,28 @@
  * - ::nc_server_config_add_tls_ctn()
  * - ::nc_server_config_del_tls_ctn()
  *
+* UNIX Socket
+ * ===========
+ *
+ * A UNIX socket endpoint can be established using one of two mechanisms:
+ *
+ * 1) **Cleartext Path**: The filesystem path is explicitly stored in the configuration.
+ * To use this, pass a valid path string to ::nc_server_config_add_unix_socket().
+ *
+ * 2) **Hidden Path**: The filesystem path is managed via the API and is not visible
+ * in the YANG configuration. To use this, pass NULL as the path argument to
+ * ::nc_server_config_add_unix_socket(). The actual runtime path must then be set
+ * using ::nc_server_set_unix_socket_path().
+ *
+ * Security Recommendation
+ * -----------------------
+ * The **Hidden Path** (Option 2) is strongly recommended.
+ *
+ * If Cleartext paths are enabled, any user with permission to modify the server
+ * configuration can change the UNIX socket path via YANG. This allows them to
+ * force the server to create or overwrite arbitrary files on the filesystem
+ * with the privileges of the server process.
+ *
  * FD
  * ==
  *

examples/server.c

@@ -235,13 +235,19 @@ init(const char *unix_socket_path, struct ly_ctx **context, struct nc_pollsessio
         ERR_MSG_CLEANUP("Error while parsing the example configuration data.\n");
     }
 
-    /* add UNIX socket to the configuration tree if the path was specified */
     if (unix_socket_path) {
+        /* add UNIX socket endpoint to the configuration tree if the path was specified */
         rc = nc_server_config_add_unix_socket(*context, "unix-socket-endpt",
-                unix_socket_path, NULL, NULL, NULL, &config);
+                NULL, NULL, NULL, NULL, &config);
         if (rc) {
             ERR_MSG_CLEANUP("Creating UNIX socket endpoint configuration failed.\n");
         }
+
+        /* use the specified path for the UNIX socket endpoint */
+        rc = nc_server_set_unix_socket_path("unix-socket-endpt", unix_socket_path);
+        if (rc) {
+            ERR_MSG_CLEANUP("Setting UNIX socket path failed.\n");
+        }
     }
 
     /* since nc_server_config_setup_data() requires all implicit nodes to be present and the example

modules/libnetconf2-netconf-server@2025-11-11.yang

@@ -51,6 +51,13 @@ module libnetconf2-netconf-server {
     description "Second revision.";
   }
 
+  // Features
+
+  feature unix-socket-path {
+    description
+      "Indicates that the server supports configuration of the UNIX socket path.";
+    }
+
   // Identities
 
 /*
@@ -310,17 +317,31 @@ module libnetconf2-netconf-server {
            and listen for incoming NETCONF connections. Client authentication
            is based on the connecting process's effective user ID.";
 
-        leaf path {
-          type string {
-            length "1..107";
-          }
+        choice socket-path-config {
           mandatory true;
           description
-            "Filesystem path where the UNIX socket will be created.
-             The parent directory
-             must exist and be writable by the NETCONF server process.
+            "Selects how the UNIX domain socket path is determined.";
+          case socket-path {
+            if-feature "unix-socket-path";
+            leaf socket-path {
+              type string {
+                length "1..107";
+              }
+              description
+                "Relative filesystem path where the UNIX socket will be bound.
+                 The parent directory must be set by an internal server API setting.
 
-             Example: /var/run/netconf.sock";
+                 Example: netconf.sock";
+            }
+          }
+          case hidden-path {
+            leaf hidden-path {
+              type empty;
+              description
+                "Indicates that the UNIX socket path is not configured via YANG, but is instead
+                 determined by internal server API settings.";
+            }
+          }
         }
 
         container socket-permissions {

src/server_config.c

@@ -360,6 +360,7 @@ nc_server_config_free(struct nc_server_config *config)
     struct nc_ch_client *ch_client;
     struct nc_ch_endpt *ch_endpt;
     LY_ARRAY_COUNT_TYPE i, j;
+    char *socket_path = NULL;
 
     if (!config) {
         return;
@@ -375,18 +376,32 @@ nc_server_config_free(struct nc_server_config *config)
     LY_ARRAY_FOR(config->endpts, i) {
         endpt = &config->endpts[i];
 
+        if (endpt->ti == NC_TI_UNIX) {
+            /* get the socket path before freeing the name */
+            socket_path = nc_server_unix_get_socket_path(endpt);
+        }
+
         free(endpt->name);
 
         /* free binds */
         LY_ARRAY_FOR(endpt->binds, j) {
-            free(endpt->binds[j].address);
             if (endpt->binds[j].sock != -1) {
                 close(endpt->binds[j].sock);
+                if (socket_path) {
+                    /* remove the UNIX socket file */
+                    unlink(socket_path);
+                }
             }
+            free(endpt->binds[j].address);
             pthread_mutex_destroy(&endpt->bind_lock);
         }
         LY_ARRAY_FREE(endpt->binds);
 
+        if (endpt->ti == NC_TI_UNIX) {
+            free(socket_path);
+            socket_path = NULL;
+        }
+
         /* free transport specific options */
         switch (endpt->ti) {
 #ifdef NC_ENABLED_SSH_TLS
@@ -2851,26 +2866,68 @@ config_tls(const struct lyd_node *node, enum nc_operation parent_op, struct nc_e
 #endif /* NC_ENABLED_SSH_TLS */
 
 static int
-config_unix_path(const struct lyd_node *node, enum nc_operation parent_op, struct nc_endpt *endpt)
+config_unix_socket_path(const struct lyd_node *node, enum nc_operation parent_op, struct nc_endpt *endpt)
 {
     enum nc_operation op;
     struct nc_bind *bind;
+    struct nc_server_unix_opts *opts;
 
     NC_NODE_GET_OP(node, parent_op, &op);
 
+    opts = endpt->opts.unix;
+
     if (op == NC_OP_DELETE) {
         /* the endpoint must have a single binding, so we can just free it,
          * the socket will be closed in ::nc_server_config_free() */
         assert(endpt->binds);
         free(endpt->binds[0].address);
         LY_ARRAY_FREE(endpt->binds);
+
+        /* also clear the cleartext path flag */
+        opts->path_type = NC_UNIX_SOCKET_PATH_UNKNOWN;
     } else if ((op == NC_OP_CREATE) || (op == NC_OP_REPLACE)) {
         /* the endpoint must not have any bindings yet, so we can just create one */
         assert(!endpt->binds);
         LY_ARRAY_NEW_RET(LYD_CTX(node), endpt->binds, bind, 1);
         bind->address = strdup(lyd_get_value(node));
         NC_CHECK_ERRMEM_RET(!bind->address, 1);
         bind->sock = -1;
+
+        /* also set the cleartext path flag */
+        opts->path_type = NC_UNIX_SOCKET_PATH_FILE;
+    }
+
+    return 0;
+}
+
+static int
+config_unix_hidden_path(const struct lyd_node *node, enum nc_operation parent_op, struct nc_endpt *endpt)
+{
+    enum nc_operation op;
+    struct nc_bind *bind;
+    struct nc_server_unix_opts *opts;
+
+    NC_NODE_GET_OP(node, parent_op, &op);
+
+    opts = endpt->opts.unix;
+
+    if (op == NC_OP_DELETE) {
+        /* the endpoint must have a single binding, so we can just free it,
+         * the socket will be closed in ::nc_server_config_free() */
+        assert(endpt->binds);
+        LY_ARRAY_FREE(endpt->binds);
+
+        /* also clear the hidden path flag */
+        opts->path_type = NC_UNIX_SOCKET_PATH_UNKNOWN;
+    } else if ((op == NC_OP_CREATE) || (op == NC_OP_REPLACE)) {
+        /* the endpoint must not have any bindings yet, so we can just create one
+         * and since the path is hidden, there is no address to set */
+        assert(!endpt->binds);
+        LY_ARRAY_NEW_RET(LYD_CTX(node), endpt->binds, bind, 1);
+        bind->sock = -1;
+
+        /* also set the hidden path flag */
+        opts->path_type = NC_UNIX_SOCKET_PATH_HIDDEN;
     }
 
     return 0;
@@ -3117,7 +3174,7 @@ config_unix_client_auth(const struct lyd_node *node, enum nc_operation parent_op
 static int
 config_unix(const struct lyd_node *node, enum nc_operation parent_op, struct nc_endpt *endpt)
 {
-    struct lyd_node *n;
+    struct lyd_node *n, *socket_path = NULL, *hidden_path = NULL;
     enum nc_operation op;
 
     NC_NODE_GET_OP(node, parent_op, &op);
@@ -3135,9 +3192,15 @@ config_unix(const struct lyd_node *node, enum nc_operation parent_op, struct nc_
         endpt->opts.unix->gid = (gid_t)-1;
     }
 
-    /* config path */
-    NC_CHECK_RET(nc_lyd_find_child(node, "path", 1, &n));
-    NC_CHECK_RET(config_unix_path(n, op, endpt));
+    /* config mandatory unix socket path choice => only one of them can be present */
+    NC_CHECK_RET(nc_lyd_find_child(node, "socket-path", 0, &socket_path));
+    NC_CHECK_RET(nc_lyd_find_child(node, "hidden-path", 0, &hidden_path));
+    if (socket_path) {
+        NC_CHECK_RET(config_unix_socket_path(socket_path, op, endpt));
+    } else {
+        assert(hidden_path);
+        NC_CHECK_RET(config_unix_hidden_path(hidden_path, op, endpt));
+    }
 
     /* config socket permissions */
     NC_CHECK_RET(nc_lyd_find_child(node, "socket-permissions", 1, &n));
@@ -4962,6 +5025,57 @@ nc_server_config_libnetconf2_netconf_server(const struct lyd_node *tree, int is_
     return rc;
 }
 
+/**
+ * @brief Check if two server endpoint bindings match.
+ *
+ * They match if they use the same transport protocol, address and port.
+ *
+ * @param[in] e1 First server endpoint.
+ * @param[in] b1 First server endpoint binding.
+ * @param[in] e2 Second server endpoint.
+ * @param[in] b2 Second server endpoint binding.
+ * @return 1 if they match, 0 otherwise.
+ */
+static int
+nc_server_config_bindings_match(const struct nc_endpt *e1, const struct nc_bind *b1,
+        const struct nc_endpt *e2, const struct nc_bind *b2)
+{
+    int rc = 1;
+    char *addr1 = NULL, *addr2 = NULL;
+
+    if (e1->ti != e2->ti) {
+        /* different transport protocols */
+        return 0;
+    }
+
+    if (e1->ti == NC_TI_UNIX) {
+        /* UNIX sockets may have hidden or cleartext addresses */
+        addr1 = nc_server_unix_get_socket_path(e1);
+        addr2 = nc_server_unix_get_socket_path(e2);
+    } else {
+        addr1 = b1->address;
+        addr2 = b2->address;
+    }
+    if (!addr1 || !addr2) {
+        /* unable to get the address */
+        rc = 0;
+        goto cleanup;
+    }
+
+    if (strcmp(addr1, addr2) || (b1->port != b2->port)) {
+        /* different addresses or ports */
+        rc = 0;
+        goto cleanup;
+    }
+
+cleanup:
+    if (e1->ti == NC_TI_UNIX) {
+        free(addr1);
+        free(addr2);
+    }
+    return rc;
+}
+
 /**
  * @brief Atomically starts listening on new sockets and reuses existing ones.
  *
@@ -4989,7 +5103,7 @@ nc_server_config_reconcile_sockets_listen(struct nc_server_config *old_cfg,
             found = 0;
             LY_ARRAY_FOR(old_cfg->endpts, struct nc_endpt, old_endpt) {
                 LY_ARRAY_FOR(old_endpt->binds, struct nc_bind, old_bind) {
-                    if (!strcmp(new_bind->address, old_bind->address) && (new_bind->port == old_bind->port)) {
+                    if (nc_server_config_bindings_match(new_endpt, new_bind, old_endpt, old_bind)) {
                         /* match found, reuse the socket */
                         new_bind->sock = old_bind->sock;
                         found = 1;
@@ -5510,6 +5624,8 @@ nc_server_config_unix_dup(const struct nc_server_unix_opts *src, struct nc_serve
     *dst = calloc(1, sizeof **dst);
     NC_CHECK_ERRMEM_RET(!*dst, 1);
 
+    (*dst)->path_type = src->path_type;
+
     (*dst)->mode = src->mode;
     (*dst)->uid = src->uid;
     (*dst)->gid = src->gid;
@@ -5739,8 +5855,10 @@ nc_server_config_dup(const struct nc_server_config *src, struct nc_server_config
         /* binds */
         LN2_LY_ARRAY_CREATE_GOTO_WRAP(dst_endpt->binds, LY_ARRAY_COUNT(src_endpt->binds), rc, cleanup);
         LY_ARRAY_FOR(src_endpt->binds, j) {
-            dst_endpt->binds[j].address = strdup(src_endpt->binds[j].address);
-            NC_CHECK_ERRMEM_GOTO(!dst_endpt->binds[j].address, rc = 1, cleanup);
+            if (src_endpt->binds[j].address) {
+                dst_endpt->binds[j].address = strdup(src_endpt->binds[j].address);
+                NC_CHECK_ERRMEM_GOTO(!dst_endpt->binds[j].address, rc = 1, cleanup);
+            }
             dst_endpt->binds[j].port = src_endpt->binds[j].port;
 
             /* mark the socket as uninitialized, it will be reassigned in ::nc_server_config_reconcile_sockets_listen() */

src/server_config_util.c

@@ -238,12 +238,31 @@ nc_server_config_add_unix_socket(const struct ly_ctx *ctx, const char *endpt_nam
 {
     int rc = 0;
     char *path_fmt = NULL;
+    struct lys_module *mod;
+    const char *path_type_str;
 
-    NC_CHECK_ARG_RET(NULL, ctx, path, config, 1);
+    NC_CHECK_ARG_RET(NULL, ctx, config, 1);
 
-    /* create the path to the socket's path */
+    if (!path) {
+        /* creating a hidden UNIX socket path set by other means */
+        path_type_str = "hidden-path";
+    } else {
+        /* creating a standard UNIX socket path */
+        path_type_str = "socket-path";
+
+        /* check if the 'unix-socket-path' feature is enabled in the libnetconf2-netconf-server module */
+        mod = ly_ctx_get_module_implemented(ctx, "libnetconf2-netconf-server");
+        NC_CHECK_RET(!mod, 1);
+        if (lys_feature_value(mod, "unix-socket-path")) {
+            ERR(NULL, "Unable to set UNIX socket path ('unix-socket-path' feature not enabled in "
+                    "'libnetconf2-netconf-server' module).");
+            return 1;
+        }
+    }
+
+    /* create the path to UNIX socket or just the empty leaf for hidden path */
     NC_CHECK_ERR_RET(asprintf(&path_fmt, "/ietf-netconf-server:netconf-server/listen/endpoints/endpoint[name='%s']/"
-            "libnetconf2-netconf-server:unix/path", endpt_name) == -1, ERRMEM, 1);
+            "libnetconf2-netconf-server:unix/%s", endpt_name, path_type_str) == -1, ERRMEM, 1);
     NC_CHECK_GOTO(rc = nc_server_config_create(ctx, config, path, path_fmt), cleanup);
 
     if (!mode && !owner && !group) {