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Some functions return a pointer to an object that cannot be modified without causing undefined behavior. These functions include getenv(), setlocale(), localeconv(), asctime(), and strerror(). In such cases, the function call results must be treated as being const-qualified.

The C Standard, 7.2224.4.6, paragraph 4 [ISO/IEC 9899:20112024], defines getenv() as follows:

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If the string returned by getenv() must be altered, a local copy should be created. Altering the string returned by getenv() is undefined behavior. (see See undefined behavior 184.).

Similarly, subclause 7.11.1.1, paragraph 8 [ISO/IEC 9899:20112024], defines setlocale() as follows:

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 And subclause 7.11.2.1, paragraph 8 [ISO/IEC 9899:20112024], defines localeconv() as follows:

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Altering the string returned by setlocale() or the structure returned by localeconv() are undefined behaviors. (see See undefined behaviors 120 and 121.) . Furthermore, the C Standard imposes no requirements on the contents of the string by setlocale(). Consequently, no assumptions can be made as to the string's internal contents or structure.

Finally, subclause 7.2426.6.23, paragraph 4 4 [ISO/IEC 9899:20112024], states:

The The strerror function returns a pointer to the string, the contents of which are locale-specific. The array pointed to shall not be modified by the program, but may be overwritten by . The behavior is undefined if the returned value is used after a subsequent call to the strerror functionthe strerror function, or after the thread which called the function to obtain the returned value has exited.

Altering the string returned by strerror() is undefined behavior. (see See undefined behavior 184.).

Noncompliant Code Example (getenv())

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If the programmer does not intend to modify the environment, this compliant solution demonstrates modifying how to modify a copy of the return value:

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Modifying the object pointed to by the return value of getenv(), setlocale(), localeconv(), asctime(), or strerror() is undefined behavior. Even if the modification succeeds, the modified object can be overwritten by a subsequent call to the same function.

Automated Detection

Related Vulnerabilities

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Bibliography

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