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This code example is noncompliant because the string referenced by tmpvar may be overwritten as a result of the second call to the getenv() function. As a result, it is possible that both tmpvar and tempvar will compare equal even if the two environment variables have different values.

Compliant Solution

This compliant solution uses only the C malloc() and strcpy() functions to copy the string returned by getenv() into a dynamically allocated buffer:

char *tmpvar;
char *tempvar;

const char *temp = getenv("TMP");
if (temp != NULL) {
  tmpvar = (char *)malloc(strlen(temp)+1);
  if (tmpvar != NULL) {
    strcpy(tmpvar, temp);
  } else {
    /* Handle error */
  }
} else {
  /* Handle error */
}

temp = getenv("TEMP");
if (temp != NULL) {
  tempvar = (char *)malloc(strlen(temp)+1);
  if (tempvar != NULL) {
    strcpy(tempvar, temp);
  } else {
    /* Handle error */
  }
} else {
  /* Handle error */
}

if (strcmp(tmpvar, tempvar) == 0) {
  printf("TMP and TEMP are the same.\n");
} else {
  printf("TMP and TEMP are NOT the same.\n");
}
free(tmpvar);
tmpvar = NULL;
free(tempvar);
tempvar = NULL;

Compliant Solution (C11 Annex K)

C11 Annex K provides the getenv_s()function for getting a value from the current environment [ISO/IEC 9899:2011].  However, note that according to the standard, getenv_s() can still have data races with other threads of execution which modify the environment list.

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char *tmpvar;
char *tempvar;

const char *temp = getenv("TMP");
if (temp != NULL) {
  tmpvar = strdup(temp);
  if (tmpvar == NULL) {
    /* Handle error */
  }
} else {
  /* Handle error */
}

temp = getenv("TEMP");
if (temp != NULL) {
  tempvar = strdup(temp);
  if (tempvar == NULL) {
    /* Handle error */
  }
} else {
  /* Handle error */
}

if (strcmp(tmpvar, tempvar) == 0) {
  printf("TMP and TEMP are the same.\n");
} else {
  printf("TMP and TEMP are NOT the same.\n");
}
free(tmpvar);
tmpvar = NULL;
free(tempvar);
tempvar = NULL;

Compliant Solution

This compliant solution uses only the C malloc() and strcpy() functions to copy the string returned by getenv() into a dynamically allocated buffer:

char *tmpvar;
char *tempvar;

const char *temp = getenv("TMP");
if (temp != NULL) {
  tmpvar = (char *)malloc(strlen(temp)+1);
  if (tmpvar != NULL) {
    strcpy(tmpvar, temp);
  } else {
    /* Handle error */
  }
} else {
  /* Handle error */
}

temp = getenv("TEMP");
if (temp != NULL) {
  tempvar = (char *)malloc(strlen(temp)+1);
  if (tempvar != NULL) {
    strcpy(tempvar, temp);
  } else {
    /* Handle error */
  }
} else {
  /* Handle error */
}

if (strcmp(tmpvar, tempvar) == 0) {
  printf("TMP and TEMP are the same.\n");
} else {
  printf("TMP and TEMP are NOT the same.\n");
}
free(tmpvar);
tmpvar = NULL;
free(tempvar);
tempvar = NULL;

Risk Assessment

Storing the pointer to the string returned by getenv() can result in overwritten environmental data.

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