Use a control socket directory to restrict access

[tinc] / src / tincctl.c

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;
        }