CertC-CON30ΒΆ

Clean up thread-specific storage

Required inputs: IR

The tss_create() function creates a thread-specific storage pointer identified by a key. Threads can allocate thread-specific storage and associate the storage with a key that uniquely identifies the storage by calling the tss_set() function. If not properly freed, this memory may be leaked. Ensure that thread-specific storage is freed.

Noncompliant Code Example

In this noncompliant code example, each thread dynamically allocates storage in the get_data() function, which is then associated with the global key by the call to tss_set() in the add_data() function. This memory is subsequently leaked when the threads terminate. 

#include <threads.h>
#include <stdlib.h>

/* Global key to the thread-specific storage */
tss_t key;
enum { MAX_THREADS = 3 };

int *get_data(void) {
  int *arr = (int *)malloc(2 * sizeof(int));
  if (arr == NULL) {
    return arr;  /* Report error  */
  }
  arr[0] = 10;
  arr[1] = 42;
  return arr;
}

int add_data(void) {
  int *data = get_data();
  if (data == NULL) {
    return -1;       /* Report error */
  }

  if (thrd_success != tss_set(key, (void *)data)) {
    /* Handle error */
  }
  return 0;
}

void print_data(void) {
  /* Get this thread's global data from key */
  int *data = tss_get(key);

  if (data != NULL) {
    /* Print data */
  }
}

int function(void *dummy) {
  if (add_data() != 0) {
    return -1;       /* Report error */
  }
  print_data();
  return 0;
}

int main(void) {
  thrd_t thread_id[MAX_THREADS];

  /* Create the key before creating the threads */
  if (thrd_success != tss_create(&key, NULL)) {
    /* Handle error */
  }

  /* Create threads that would store specific storage */
  for (size_t i = 0; i < MAX_THREADS; i++) {
    if (thrd_success != thrd_create(&thread_id[i], function, NULL)) {
      /* Handle error */
    }
  }

  for (size_t i = 0; i < MAX_THREADS; i++) {
    if (thrd_success != thrd_join(thread_id[i], NULL)) {
      /* Handle error */
    }
  }

  tss_delete(key);
  return 0;
}
Compliant Solution

In this compliant solution, each thread explicitly frees the thread-specific storage returned by the tss_get() function before terminating: 

#include <threads.h>
#include <stdlib.h>

/* Global key to the thread-specific storage */
tss_t key;

int function(void *dummy) {
  if (add_data() != 0) {
    return -1;       /* Report error */
  }
  print_data();
  free(tss_get(key));
  return 0;
}

/* ... Other functions are unchanged */
Compliant Solution

This compliant solution invokes a destructor function registered during the call to tss_create() to automatically free any thread-specific storage: 

#include <threads.h>
#include <stdlib.h>

/* Global key to the thread-specific storage */
tss_t key;
enum { MAX_THREADS = 3 };

/* ... Other functions are unchanged */

void destructor(void *data) {
  free(data);
}
 
int main(void) {
  thrd_t thread_id[MAX_THREADS];

  /* Create the key before creating the threads */
  if (thrd_success != tss_create(&key, destructor)) {
    /* Handle error */
  }

  /* Create threads that would store specific storage */
  for (size_t i = 0; i < MAX_THREADS; i++) {
    if (thrd_success != thrd_create(&thread_id[i], function, NULL)) {
      /* Handle error */
    }
  }

  for (size_t i = 0; i < MAX_THREADS; i++) {
    if (thrd_success != thrd_join(thread_id[i], NULL)) {
      /* Handle error */
    }
  }

  tss_delete(key);
  return 0;
}


Risk Assessment

Failing to free thread-specific objects results in memory leaks and could result in a denial-of-service attack.

Rule Severity Likelihood Remediation Cost Priority Level
CON30-C Medium Unlikely Medium P4 L3
Excerpt from SEI CERT C Coding Standard: Rules for Developing Safe, Reliable, and Secure Systems (2016 Edition) and SEI CERT C Coding Standard [https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/concurrency-con/con30-c], Copyright (C) 1995-2026 Carnegie Mellon University. See section 9.4. "3rd-Party Licenses" in the documentation for full details.

Possible Messages

Key

Text

Severity

Disabled

cleanup_thread_specific_storage

Clean up thread-specific storage.

None

False

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