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 <pthread.h>
  13 #include <urcu/system.h>
  14 #include "common/logging.h"
  15 #include "common/macros.h"
  16 #include "common/getenv.h"
  17
  18 enum lttng_env_secure {
  19         LTTNG_ENV_SECURE,
  20         LTTNG_ENV_NOT_SECURE,
  21 };
  22
  23 struct lttng_env {
  24         const char *key;
  25         enum lttng_env_secure secure;
  26         char *value;
  27 };
  28
  29 /* lttng_ust_getenv_init_mutex provides mutual exclusion for initialization. */
  30 static pthread_mutex_t lttng_ust_getenv_init_mutex = PTHREAD_MUTEX_INITIALIZER;
  31 static int lttng_ust_getenv_is_init = 0;
  32
  33 static struct lttng_env lttng_env[] = {
  34         /*
  35          * LTTNG_UST_DEBUG and LTTNG_UST_ABORT_ON_CRITICAL are used directly by
  36          * the internal logging, because they need to be already set for ERR()
  37          * used in lttng_ust_getenv_init().
  38          */
  39         { "LTTNG_UST_DEBUG", LTTNG_ENV_NOT_SECURE, NULL, },
  40         { "LTTNG_UST_ABORT_ON_CRITICAL", LTTNG_ENV_NOT_SECURE, NULL, },
  41
  42         /* Env. var. which can be used in setuid/setgid executables. */
  43         { "LTTNG_UST_WITHOUT_BADDR_STATEDUMP", LTTNG_ENV_NOT_SECURE, NULL, },
  44         { "LTTNG_UST_REGISTER_TIMEOUT", LTTNG_ENV_NOT_SECURE, NULL, },
  45
  46         /* Env. var. which are not fetched in setuid/setgid executables. */
  47         { "LTTNG_UST_CLOCK_PLUGIN", LTTNG_ENV_SECURE, NULL, },
  48         { "LTTNG_UST_GETCPU_PLUGIN", LTTNG_ENV_SECURE, NULL, },
  49         { "LTTNG_UST_ALLOW_BLOCKING", LTTNG_ENV_SECURE, NULL, },
  50         { "HOME", LTTNG_ENV_SECURE, NULL, },
  51         { "LTTNG_HOME", LTTNG_ENV_SECURE, NULL, },
  52         { "LTTNG_UST_APP_PATH", LTTNG_ENV_SECURE, NULL, },
  53 };
  54
  55 static
  56 int lttng_is_setuid_setgid(void)
  57 {
  58         return geteuid() != getuid() || getegid() != getgid();
  59 }
  60
  61 /*
  62  * Wrapper over getenv that will only return the values of whitelisted
  63  * environment variables when the current process is setuid and/or setgid.
  64  */
  65 char *lttng_ust_getenv(const char *name)
  66 {
  67         size_t i;
  68         struct lttng_env *e;
  69         bool found = false;
  70
  71         /*
  72          * Perform lazy initialization of lttng_ust_getenv for early use
  73          * by library constructors.
  74          */
  75         lttng_ust_getenv_init();
  76
  77         for (i = 0; i < LTTNG_ARRAY_SIZE(lttng_env); i++) {
  78                 e = &lttng_env[i];
  79
  80                 if (strcmp(e->key, name) == 0) {
  81                         found = true;
  82                         break;
  83                 }
  84         }
  85         if (!found) {
  86                 return NULL;
  87         }
  88         return e->value;
  89 }
  90
  91 void lttng_ust_getenv_init(void)
  92 {
  93         size_t i;
  94
  95         /*
  96          * Return early if the init has already completed.
  97          */
  98         if (CMM_LOAD_SHARED(lttng_ust_getenv_is_init)) {
  99                 /*
 100                  * Load lttng_ust_getenv_is_init before reading environment cache.
 101                  */
 102                 cmm_smp_rmb();
 103                 return;
 104         }
 105
 106         pthread_mutex_lock(&lttng_ust_getenv_init_mutex);
 107
 108         /*
 109          * Check again if the init has completed in another thread now that we
 110          * have acquired the mutex.
 111          */
 112         if (lttng_ust_getenv_is_init)
 113                 goto end_init;
 114
 115         for (i = 0; i < LTTNG_ARRAY_SIZE(lttng_env); i++) {
 116                 struct lttng_env *e = &lttng_env[i];
 117
 118                 if (e->secure == LTTNG_ENV_SECURE && lttng_is_setuid_setgid()) {
 119                         ERR("Getting environment variable '%s' from setuid/setgid binary refused for security reasons.",
 120                                 e->key);
 121                         continue;
 122                 }
 123                 e->value = getenv(e->key);
 124         }
 125
 126         /*
 127          * Store environment cache before setting lttng_ust_getenv_is_init to 1.
 128          */
 129         cmm_smp_wmb();
 130         CMM_STORE_SHARED(lttng_ust_getenv_is_init, 1);
 131 end_init:
 132         pthread_mutex_unlock(&lttng_ust_getenv_init_mutex);
 133 }