ENV30-C. Do not modify the string returned by getenv()

Upon successful completion, getenv() function returns a pointer to a null-terminated string containing the value of a specified environmental variable. If the specified variable cannot be found the environment of the calling process, a null pointer is returned.

Do not modify the value returned by the getenv() function. Create a copy and make your changes locally, using setenv() to update the environment when necessary. This allows the implementation to properly allocate and manage memory.

Non-Compliant Code Example

This non-compliant code example showing that modification of the string value returned by the function getenv(). Characters in env should not be changed directly.

int foo()
{
    char *env;
    env = getenv("TEST_ENV");
    env[0] = 'a';

    /*Do some more things*/

    return 0;
}

Compliant Code Solution

This is a compliant code solution. If it is necessary to modify the value of the string returned by the function getenv(), then the programmer should make a local copy of that string value, and then modify the local copy of that string. If it is necessary to propagate the changes back to the environment, use setenv().

int foo()
{
    char *env;
    char *copy_of_env;

    env = getenv("TEST_ENV");
    copy_of_env = malloc( strlen(env) + 1 );
    /* Error handling */
    strcpy(copy_of_env, env);

    copy_of_env[0] = 'a';

    /*Do some more things*/

    return 0;
}

Risk Assessment

The system will not be able to properly keep track of the size of environment variables, leading to memory management exploits.

References

[[ISO/IEC 9899-1999]] Section 7.20.4.5, "The getenv function"
[[Open Group 04]] getenv