Fix: race between lttng-ust getenv() and application setenv()

[lttng-ust.git] / liblttng-ust / getenv.c

diff --git a/liblttng-ust/getenv.c b/liblttng-ust/getenv.c
new file mode 100644 (file)
index 0000000..b4dc73a
--- /dev/null
+++ b/liblttng-ust/getenv.c
@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2017 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <sys/types.h>
+#include <usterr-signal-safe.h>
+#include <helper.h>
+#include "getenv.h"
+
+enum lttng_env_secure {
+       LTTNG_ENV_SECURE,
+       LTTNG_ENV_NOT_SECURE,
+};
+
+struct lttng_env {
+       const char *key;
+       enum lttng_env_secure secure;
+       char *value;
+};
+
+static struct lttng_env lttng_env[] = {
+       /*
+        * LTTNG_UST_DEBUG is used directly by snprintf, because it
+        * needs to be already set for ERR() used in
+        * lttng_ust_getenv_init().
+        */
+       { "LTTNG_UST_DEBUG", LTTNG_ENV_NOT_SECURE, NULL, },
+
+       /* Env. var. which can be used in setuid/setgid executables. */
+       { "LTTNG_UST_WITHOUT_BADDR_STATEDUMP", LTTNG_ENV_NOT_SECURE, NULL, },
+       { "LTTNG_UST_REGISTER_TIMEOUT", LTTNG_ENV_NOT_SECURE, NULL, },
+
+       /* Env. var. which are not fetched in setuid/setgid executables. */
+       { "LTTNG_UST_CLOCK_PLUGIN", LTTNG_ENV_SECURE, NULL, },
+       { "LTTNG_UST_GETCPU_PLUGIN", LTTNG_ENV_SECURE, NULL, },
+       { "LTTNG_UST_BLOCKING_RETRY_TIMEOUT", LTTNG_ENV_SECURE, NULL, },
+       { "HOME", LTTNG_ENV_SECURE, NULL, },
+       { "LTTNG_HOME", LTTNG_ENV_SECURE, NULL, },
+};
+
+static
+int lttng_is_setuid_setgid(void)
+{
+       return geteuid() != getuid() || getegid() != getgid();
+}
+
+char *lttng_getenv(const char *name)
+{
+       size_t i;
+       struct lttng_env *e;
+       bool found = false;
+
+       for (i = 0; i < LTTNG_ARRAY_SIZE(lttng_env); i++) {
+               e = &lttng_env[i];
+
+               if (strcmp(e->key, name) == 0) {
+                       found = true;
+                       break;
+               }
+       }
+       if (!found) {
+               return NULL;
+       }
+       return e->value;
+}
+
+void lttng_ust_getenv_init(void)
+{
+       size_t i;
+
+       for (i = 0; i < LTTNG_ARRAY_SIZE(lttng_env); i++) {
+               struct lttng_env *e = &lttng_env[i];
+
+               if (e->secure == LTTNG_ENV_SECURE && lttng_is_setuid_setgid()) {
+                       ERR("Getting environment variable '%s' from setuid/setgid binary refused for security reasons.",
+                               e->key);
+                       continue;
+               }
+               e->value = getenv(e->key);
+       }
+}