src/common/getenv.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  */
   6
   7 #include <stdlib.h>
   8 #include <unistd.h>
   9 #include <stdbool.h>
  10 #include <stddef.h>
  11 #include <sys/types.h>
  12 #include <urcu/system.h>
  13 #include "common/logging.h"
  14 #include "common/macros.h"
  15 #include "common/getenv.h"
  16
  17 enum lttng_env_secure {
  18         LTTNG_ENV_SECURE,
  19         LTTNG_ENV_NOT_SECURE,
  20 };
  21
  22 struct lttng_env {
  23         const char *key;
  24         enum lttng_env_secure secure;
  25         char *value;
  26 };
  27
  28 static
  29 int lttng_ust_getenv_is_init = 0;
  30
  31 static struct lttng_env lttng_env[] = {
  32         /*
  33          * LTTNG_UST_DEBUG is used directly by snprintf, because it
  34          * needs to be already set for ERR() used in
  35          * lttng_ust_getenv_init().
  36          */
  37         { "LTTNG_UST_DEBUG", LTTNG_ENV_NOT_SECURE, NULL, },
  38
  39         /* Env. var. which can be used in setuid/setgid executables. */
  40         { "LTTNG_UST_WITHOUT_BADDR_STATEDUMP", LTTNG_ENV_NOT_SECURE, NULL, },
  41         { "LTTNG_UST_REGISTER_TIMEOUT", LTTNG_ENV_NOT_SECURE, NULL, },
  42
  43         /* Env. var. which are not fetched in setuid/setgid executables. */
  44         { "LTTNG_UST_CLOCK_PLUGIN", LTTNG_ENV_SECURE, NULL, },
  45         { "LTTNG_UST_GETCPU_PLUGIN", LTTNG_ENV_SECURE, NULL, },
  46         { "LTTNG_UST_ALLOW_BLOCKING", LTTNG_ENV_SECURE, NULL, },
  47         { "HOME", LTTNG_ENV_SECURE, NULL, },
  48         { "LTTNG_HOME", LTTNG_ENV_SECURE, NULL, },
  49 };
  50
  51 static
  52 int lttng_is_setuid_setgid(void)
  53 {
  54         return geteuid() != getuid() || getegid() != getgid();
  55 }
  56
  57 /*
  58  * Wrapper over getenv that will only return the values of whitelisted
  59  * environment variables when the current process is setuid and/or setgid.
  60  */
  61 char *lttng_ust_getenv(const char *name)
  62 {
  63         size_t i;
  64         struct lttng_env *e;
  65         bool found = false;
  66
  67         /*
  68          * Perform lazy initialization of lttng_ust_getenv for early use
  69          * by library constructors.
  70          */
  71         lttng_ust_getenv_init();
  72
  73         for (i = 0; i < LTTNG_ARRAY_SIZE(lttng_env); i++) {
  74                 e = &lttng_env[i];
  75
  76                 if (strcmp(e->key, name) == 0) {
  77                         found = true;
  78                         break;
  79                 }
  80         }
  81         if (!found) {
  82                 return NULL;
  83         }
  84         return e->value;
  85 }
  86
  87 void lttng_ust_getenv_init(void)
  88 {
  89         size_t i;
  90
  91         if (CMM_LOAD_SHARED(lttng_ust_getenv_is_init))
  92                 return;
  93
  94         for (i = 0; i < LTTNG_ARRAY_SIZE(lttng_env); i++) {
  95                 struct lttng_env *e = &lttng_env[i];
  96
  97                 if (e->secure == LTTNG_ENV_SECURE && lttng_is_setuid_setgid()) {
  98                         ERR("Getting environment variable '%s' from setuid/setgid binary refused for security reasons.",
  99                                 e->key);
 100                         continue;
 101                 }
 102                 e->value = getenv(e->key);
 103         }
 104         CMM_STORE_SHARED(lttng_ust_getenv_is_init, 1);
 105 }