Use a control socket directory to restrict access

This provides reasonable security even on Solaris. The sysadmin is
responsible for securing the control socket's ancestors from the
grandparent on.

We could add a cryptographic handshake later if desired.

diff --git a/src/control.c b/src/control.c
index a795843..2673385 100644 (file)
--- a/src/control.c
+++ b/src/control.c
@@ -191,6 +191,7 @@ static void handle_new_control_socket(int fd, short events, void *data) {
 
        memset(&greeting, 0, sizeof greeting);
        greeting.version = TINC_CTL_VERSION_CURRENT;
+       greeting.pid = getpid();
        if(bufferevent_write(ev, &greeting, sizeof greeting) == -1) {
                logger(LOG_ERR,
                           _("Cannot send greeting for new control connection: %s"),
@@ -213,10 +214,11 @@ static int control_compare(const struct event *a, const struct event *b) {
 bool init_control() {
        int result;
        struct sockaddr_un addr;
+       char *lastslash;
 
        if(strlen(controlsocketname) >= sizeof addr.sun_path) {
                logger(LOG_ERR, _("Control socket filename too long!"));
-               return false;
+               goto bail;
        }
 
        memset(&addr, 0, sizeof addr);
@@ -227,12 +229,43 @@ bool init_control() {
 
        if(control_socket < 0) {
                logger(LOG_ERR, _("Creating UNIX socket failed: %s"), strerror(errno));
-               return false;
+               goto bail;
+       }
+
+       /*
+        * Restrict connections to our control socket by ensuring the parent
+        * directory can be traversed only by root. Note this is not totally
+        * race-free unless all ancestors are writable only by trusted users,
+        * which we don't verify.
+        */
+
+       struct stat statbuf;
+       lastslash = strrchr(controlsocketname, '/');
+       if(lastslash != NULL) {
+               *lastslash = 0; /* temporarily change controlsocketname to be dir */
+               if(mkdir(controlsocketname, 0700) < 0 && errno != EEXIST) {
+                       logger(LOG_ERR, _("Unable to create control socket directory %s: %s"), controlsocketname, strerror(errno));
+                       *lastslash = '/';
+                       goto bail;
+               }
+
+               result = stat(controlsocketname, &statbuf);
+               *lastslash = '/';
+       } else
+               result = stat(".", &statbuf);
+
+       if(result < 0) {
+               logger(LOG_ERR, _("Examining control socket directory failed: %s"), strerror(errno));
+               goto bail;
+       }
+
+       if(statbuf.st_uid != 0 || (statbuf.st_mode & S_IXOTH) != 0 || (statbuf.st_gid != 0 && (statbuf.st_mode & S_IXGRP)) != 0) {
+               logger(LOG_ERR, _("Control socket directory ownership/permissions insecure."));
+               goto bail;
        }
 
-       //unlink(controlsocketname);
        result = bind(control_socket, (struct sockaddr *)&addr, sizeof addr);
-       
+
        if(result < 0 && errno == EADDRINUSE) {
                result = connect(control_socket, (struct sockaddr *)&addr, sizeof addr);
                if(result < 0) {
@@ -240,33 +273,36 @@ bool init_control() {
                        unlink(controlsocketname);
                        result = bind(control_socket, (struct sockaddr *)&addr, sizeof addr);
                } else {
-                       close(control_socket);
                        if(netname)
                                logger(LOG_ERR, _("Another tincd is already running for net `%s'."), netname);
                        else
                                logger(LOG_ERR, _("Another tincd is already running."));
-                       return false;
+                       goto bail;
                }
        }
 
        if(result < 0) {
-               logger(LOG_ERR, _("Can't bind to %s: %s\n"), controlsocketname, strerror(errno));
-               close(control_socket);
-               return false;
+               logger(LOG_ERR, _("Can't bind to %s: %s"), controlsocketname, strerror(errno));
+               goto bail;
        }
 
        if(listen(control_socket, 3) < 0) {
-               logger(LOG_ERR, _("Can't listen on %s: %s\n"), controlsocketname, strerror(errno));
-               close(control_socket);
-               return false;
+               logger(LOG_ERR, _("Can't listen on %s: %s"), controlsocketname, strerror(errno));
+               goto bail;
        }
 
        control_socket_tree = splay_alloc_tree((splay_compare_t)control_compare, (splay_action_t)bufferevent_free);
 
        event_set(&control_event, control_socket, EV_READ | EV_PERSIST, handle_new_control_socket, NULL);
        event_add(&control_event, NULL);
-
        return true;
+
+bail:
+       if(control_socket != -1) {
+               close(control_socket);
+               control_socket = -1;
+       }
+       return false;
 }
 
 void exit_control() {

diff --git a/src/control_common.h b/src/control_common.h
index 0975826..6384651 100644 (file)
--- a/src/control_common.h
+++ b/src/control_common.h
@@ -41,6 +41,7 @@ enum request_type {
 /* This greeting is sent by the server on socket open. */
 typedef struct tinc_ctl_greeting_t {
        int version;
+       pid_t pid;
 } tinc_ctl_greeting_t;
 
 /* A single request or response header. */

diff --git a/src/tincctl.c b/src/tincctl.c
index 7e08629..aed1c31 100644 (file)
--- a/src/tincctl.c
+++ b/src/tincctl.c
@@ -319,7 +319,7 @@ static void make_names(void) {
 #endif
 
        if(!controlsocketname)
-               asprintf(&controlsocketname, LOCALSTATEDIR "/run/%s.control", identname);
+               asprintf(&controlsocketname, "%s/run/%s.control/socket", LOCALSTATEDIR, identname);
 
        if(netname) {
                if(!confbase)
@@ -439,10 +439,11 @@ static int send_ctl_request_cooked(int fd, enum request_type type,
 
 int main(int argc, char *argv[], char *envp[]) {
        struct sockaddr_un addr;
-       int fd;
-       int len;
        tinc_ctl_greeting_t greeting;
        tinc_ctl_request_t req;
+       int fd;
+       int len;
+       int result;
 
        program_name = argv[0];
 
@@ -491,7 +492,32 @@ int main(int argc, char *argv[], char *envp[]) {
                return 1;
        }
 
-       // Now handle commands that do involve connecting to a running tinc daemon.
+       /*
+        * Now handle commands that do involve connecting to a running tinc daemon.
+        * Authenticate the server by ensuring the parent directory can be
+        * traversed only by root. Note this is not totally race-free unless all
+        * ancestors are writable only by trusted users, which we don't verify.
+        */
+
+       struct stat statbuf;
+       char *lastslash = strrchr(controlsocketname, '/');
+       if(lastslash != NULL) {
+               /* control socket is not in cwd; stat its parent */
+               *lastslash = 0;
+               result = stat(controlsocketname, &statbuf);
+               *lastslash = '/';
+       } else
+               result = stat(".", &statbuf);
+
+       if(result < 0) {
+               fprintf(stderr, _("Unable to check control socket directory permissions: %s\n"), strerror(errno));
+               return 1;
+       }
+
+       if(statbuf.st_uid != 0 || (statbuf.st_mode & S_IXOTH) != 0 || (statbuf.st_gid != 0 && (statbuf.st_mode & S_IXGRP)) != 0) {
+               fprintf(stderr, _("Insecure permissions on control socket directory\n"));
+               return 1;
+       }
 
        if(strlen(controlsocketname) >= sizeof addr.sun_path) {
                fprintf(stderr, _("Control socket filename too long!\n"));
@@ -525,16 +551,8 @@ int main(int argc, char *argv[], char *envp[]) {
                return 1;
        }
 
-       struct ucred cred;
-       socklen_t credlen = sizeof cred;
-
-       if(getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cred, &credlen) < 0) {
-               fprintf(stderr, _("Could not obtain PID: %s\n"), strerror(errno));
-               return 1;
-       }
-
        if(!strcasecmp(argv[optind], "pid")) {
-               printf("%d\n", cred.pid);
+               printf("%d\n", greeting.pid);
                return 0;
        }
 

diff --git a/src/tincd.c b/src/tincd.c
index c0be975..2044310 100644 (file)
--- a/src/tincd.c
+++ b/src/tincd.c
@@ -218,7 +218,7 @@ static void make_names(void)
 #endif
 
        if(!controlsocketname)
-               asprintf(&controlsocketname, LOCALSTATEDIR "/run/%s.control", identname);
+               asprintf(&controlsocketname, "%s/run/%s.control/socket", LOCALSTATEDIR, identname);
 
        if(!logfilename)
                asprintf(&logfilename, LOCALSTATEDIR "/log/%s.log", identname);