Fix: validate file path creds in autoload mode

[lttng-tools.git] / src / common / config / config.c

diff --git a/src/common/config/config.c b/src/common/config/config.c
index 39cd57bd26038d0dd159b187440676ce836aa50d..bfb2576f4d5bab954b37958d7c1d672bcbfd7c13 100644 (file)
--- a/src/common/config/config.c
+++ b/src/common/config/config.c
@@ -2338,6 +2338,31 @@ error:
        return ret;
 }
 
+/*
+ * Return 1 if the given path is readable by the current UID or 0 if not.
+ * Return -1 if the path is EPERM.
+ */
+static int validate_file_read_creds(const char *path)
+{
+       int ret;
+
+       assert(path);
+
+       /* Can we read the file. */
+       ret = access(path, R_OK);
+       if (!ret) {
+               goto valid;
+       }
+       if (errno == EACCES) {
+               return -1;
+       } else {
+               /* Invalid. */
+               return 0;
+       }
+valid:
+       return 1;
+}
+
 static
 int load_session_from_file(const char *path, const char *session_name,
        struct session_config_validation_ctx *validation_ctx, int override)
@@ -2346,14 +2371,17 @@ int load_session_from_file(const char *path, const char *session_name,
        xmlDocPtr doc = NULL;
        xmlNodePtr sessions_node;
        xmlNodePtr session_node;
-       struct stat sb;
 
        assert(path);
        assert(validation_ctx);
 
-       ret = stat(path, &sb);
-       if (ret) {
-               ret = -LTTNG_ERR_LOAD_SESSION_NOENT;
+       ret = validate_file_read_creds(path);
+       if (ret != 1) {
+               if (ret == -1) {
+                       ret = -LTTNG_ERR_EPERM;
+               } else {
+                       ret = -LTTNG_ERR_LOAD_SESSION_NOENT;
+               }
                goto end;
        }
 
@@ -2504,11 +2532,46 @@ end:
        return ret;
 }
 
+/*
+ * Validate that the given path's credentials and the current process have the
+ * same UID. If so, return 1 else return 0 if it does NOT match.
+ */
+static int validate_path_creds(const char *path)
+{
+       int ret, uid = getuid();
+       struct stat buf;
+
+       assert(path);
+
+       if (uid == 0) {
+               goto valid;
+       }
+
+       ret = stat(path, &buf);
+       if (ret < 0) {
+               if (errno != ENOENT) {
+                       PERROR("stat");
+               }
+               ret = -LTTNG_ERR_INVALID;
+               goto valid;
+       }
+
+       if (buf.st_uid != uid) {
+               goto invalid;
+       }
+
+valid:
+       return 1;
+invalid:
+       return 0;
+}
+
 LTTNG_HIDDEN
 int config_load_session(const char *path, const char *session_name,
-               int override)
+               int override, unsigned int autoload)
 {
        int ret;
+       const char *path_ptr = NULL;
        struct session_config_validation_ctx validation_ctx = { 0 };
 
        ret = init_session_config_validation_ctx(&validation_ctx);
@@ -2517,34 +2580,77 @@ int config_load_session(const char *path, const char *session_name,
        }
 
        if (!path) {
+               char *home_path;
+               const char *sys_path;
+
                /* Try home path */
-               char *home_path = utils_get_home_dir();
+               home_path = utils_get_home_dir();
                if (home_path) {
-                       char *path;
+                       char path[PATH_MAX];
 
-                       ret = asprintf(&path, DEFAULT_SESSION_HOME_CONFIGPATH,
-                               home_path);
-                       if (ret < 0) {
-                               goto end;
-                       }
+                       /*
+                        * Try user session configuration path. Ignore error here so we can
+                        * continue loading the system wide sessions.
+                        */
+                       if (autoload) {
+                               ret = snprintf(path, sizeof(path),
+                                               DEFAULT_SESSION_HOME_CONFIGPATH "/"
+                                               DEFAULT_SESSION_CONFIG_AUTOLOAD, home_path);
+                               if (ret < 0) {
+                                       PERROR("snprintf session autoload home config path");
+                                       goto end;
+                               }
 
-                       ret = load_session_from_path(path, session_name,
-                               &validation_ctx, 0);
-                       if (!ret || (ret && ret != -LTTNG_ERR_LOAD_SESSION_NOENT)) {
-                               /* Session found or an error occured */
-                               free(path);
-                               goto end;
+                               /*
+                                * Credentials are only validated for the autoload in order to
+                                * avoid any user session daemon to try to load kernel sessions
+                                * automatically and failing all the times.
+                                */
+                               ret = validate_path_creds(path);
+                               if (ret) {
+                                       path_ptr = path;
+                               }
+                       } else {
+                               ret = snprintf(path, sizeof(path),
+                                               DEFAULT_SESSION_HOME_CONFIGPATH, home_path);
+                               if (ret < 0) {
+                                       PERROR("snprintf session home config path");
+                                       goto end;
+                               }
+                               path_ptr = path;
                        }
+                       if (path_ptr) {
+                               ret = load_session_from_path(path_ptr, session_name,
+                                               &validation_ctx, override);
+                               if (ret && ret != -LTTNG_ERR_LOAD_SESSION_NOENT) {
+                                       goto end;
+                               }
+                               /*
+                                * Continue even if the session was found since we have to try
+                                * the system wide sessions.
+                                */
+                       }
+               }
 
-                       free(path);
+               /* Reset path pointer for the system wide dir. */
+               path_ptr = NULL;
+
+               /* Try system wide configuration directory. */
+               if (autoload) {
+                       sys_path = DEFAULT_SESSION_SYSTEM_CONFIGPATH "/"
+                               DEFAULT_SESSION_CONFIG_AUTOLOAD;
+                       ret = validate_path_creds(sys_path);
+                       if (ret) {
+                               path_ptr = sys_path;
+                       }
+               } else {
+                       sys_path = DEFAULT_SESSION_SYSTEM_CONFIGPATH;
+                       path_ptr = sys_path;
                }
 
-               /* Try system session configuration path */
-               ret = load_session_from_path(DEFAULT_SESSION_SYSTEM_CONFIGPATH,
-                       session_name, &validation_ctx, 0);
-               if (!ret || (ret && ret != -LTTNG_ERR_LOAD_SESSION_NOENT)) {
-                       /* Session found or an error occured */
-                       goto end;
+               if (path_ptr) {
+                       ret = load_session_from_path(path_ptr, session_name,
+                                       &validation_ctx, override);
                }
        } else {
                ret = access(path, F_OK);