Use a separate lockfile to lock the configuration directory.

[meshlink] / src / meshlink.c

diff --git a/src/meshlink.c b/src/meshlink.c
index dd571190d86f53b46965e7e2f2aa5be0dd62a174..e6aea4dd3f708a644e482ee8de504414fd4c3e1d 100644 (file)
--- a/src/meshlink.c
+++ b/src/meshlink.c
@@ -903,23 +903,10 @@ static bool meshlink_setup(meshlink_handle_t *mesh) {
                return false;
        }
 
-       if(!main_config_lock(mesh)) {
-               logger(NULL, MESHLINK_ERROR, "Cannot lock main config file\n");
-               meshlink_errno = MESHLINK_ESTORAGE;
-               return false;
-       }
-
        return true;
 }
 
 static bool meshlink_read_config(meshlink_handle_t *mesh) {
-       // Open the configuration file and lock it
-       if(!main_config_lock(mesh)) {
-               logger(NULL, MESHLINK_ERROR, "Cannot lock main config file\n");
-               meshlink_errno = MESHLINK_ESTORAGE;
-               return false;
-       }
-
        config_t config;
 
        if(!main_config_read(mesh, "current", &config, mesh->config_key)) {
@@ -1104,14 +1091,11 @@ bool meshlink_encrypted_key_rotate(meshlink_handle_t *mesh, const void *new_key,
 
        devtool_keyrotate_probe(1);
 
-       main_config_unlock(mesh);
-
        // Rename confbase/current/ to confbase/old
 
        if(!config_rename(mesh, "current", "old")) {
                logger(mesh, MESHLINK_ERROR, "Cannot rename %s/current to %s/old\n", mesh->confbase, mesh->confbase);
                meshlink_errno = MESHLINK_ESTORAGE;
-               main_config_lock(mesh);
                pthread_mutex_unlock(&mesh->mutex);
                return false;
        }
@@ -1123,18 +1107,12 @@ bool meshlink_encrypted_key_rotate(meshlink_handle_t *mesh, const void *new_key,
        if(!config_rename(mesh, "new", "current")) {
                logger(mesh, MESHLINK_ERROR, "Cannot rename %s/new to %s/current\n", mesh->confbase, mesh->confbase);
                meshlink_errno = MESHLINK_ESTORAGE;
-               main_config_lock(mesh);
                pthread_mutex_unlock(&mesh->mutex);
                return false;
        }
 
        devtool_keyrotate_probe(3);
 
-       if(!main_config_lock(mesh)) {
-               pthread_mutex_unlock(&mesh->mutex);
-               return false;
-       }
-
        // Cleanup the "old" confbase sub-directory
 
        if(!config_destroy(mesh->confbase, "old")) {
@@ -1325,6 +1303,12 @@ meshlink_handle_t *meshlink_open_ex(const meshlink_open_params_t *params) {
 
        meshlink_queue_init(&mesh->outpacketqueue);
 
+       // Atomically lock the configuration directory.
+       if(!main_config_lock(mesh)) {
+               meshlink_close(mesh);
+               return NULL;
+       }
+
        // If no configuration exists yet, create it.
 
        if(!meshlink_confbase_exists(mesh)) {
@@ -1641,16 +1625,57 @@ bool meshlink_destroy(const char *confbase) {
                return false;
        }
 
-       if(!config_destroy(confbase, "current")) {
-               logger(NULL, MESHLINK_ERROR, "Cannot remove confbase sub-directories %s: %s\n", confbase, strerror(errno));
+       /* Exit early if the confbase directory itself doesn't exist */
+       if(access(confbase, F_OK) && errno == ENOENT) {
+               return true;
+       }
+
+       /* Take the lock the same way meshlink_open() would. */
+       char lockfilename[PATH_MAX];
+       snprintf(lockfilename, sizeof(lockfilename), "%s" SLASH "meshlink.lock", confbase);
+
+       FILE *lockfile = fopen(lockfilename, "w+");
+
+       if(!lockfile) {
+               logger(NULL, MESHLINK_ERROR, "Could not open lock file %s: %s", lockfilename, strerror(errno));
+               meshlink_errno = MESHLINK_ESTORAGE;
+               return false;
+       }
+
+#ifdef FD_CLOEXEC
+       fcntl(fileno(lockfile), F_SETFD, FD_CLOEXEC);
+#endif
+
+#ifdef HAVE_MINGW
+       // TODO: use _locking()?
+#else
+
+       if(flock(fileno(lockfile), LOCK_EX | LOCK_NB) != 0) {
+               logger(NULL, MESHLINK_ERROR, "Configuration directory %s still in use\n", lockfilename);
+               fclose(lockfile);
+               meshlink_errno = MESHLINK_EBUSY;
+               return false;
+       }
+
+#endif
+
+       if(!config_destroy(confbase, "current") || !config_destroy(confbase, "new") || !config_destroy(confbase, "old")) {
+               logger(NULL, MESHLINK_ERROR, "Cannot remove sub-directories in %s: %s\n", confbase, strerror(errno));
+               return false;
+       }
+
+       if(unlink(lockfilename)) {
+               logger(NULL, MESHLINK_ERROR, "Cannot remove lock file %s: %s\n", lockfilename, strerror(errno));
+               fclose(lockfile);
+               meshlink_errno = MESHLINK_ESTORAGE;
                return false;
        }
 
-       config_destroy(confbase, "new");
-       config_destroy(confbase, "old");
+       fclose(lockfile);
 
-       if(rmdir(confbase) && errno != ENOENT) {
-               logger(NULL, MESHLINK_ERROR, "Cannot remove directory %s: %s\n", confbase, strerror(errno));
+       /* TODO: do we need to remove confbase? Potential race condition? */
+       if(!sync_path(confbase)) {
+               logger(NULL, MESHLINK_ERROR, "Cannot sync directory %s: %s\n", confbase, strerror(errno));
                meshlink_errno = MESHLINK_ESTORAGE;
                return false;
        }