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