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Do not cast away a const qualification on an object of pointer type. Casting away the const qualification allows a program to modify the object referred to by the pointer, which may result in undefined behavior. See undefined behavior 6461 in Appendix J of the C Standard.

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EXP05-C-EX2: A number of C standard library functions are specified to return non-const pointers that refer to their const-qualified arguments. When the actual arguments to such functions reference const objects, attempting to use the returned non-const pointers to modify the const objects would be a violation of EXP40-C. Do not modify constant objects and would lead to undefined behavior. These functions are the following:

For instance, in following example, the function strchr returns an unqualified char* that points to the terminating null character of the constant character array s (which could be stored in ROM). Even though the pointer is not const, attempting to modify the character it points to would lead to undefined behavior.

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If the object is constant, the compiler may allocate storage in ROM or write-protected memory. Attempting to modify such an object may lead to a program crash or denial-of-service attack.

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Search for vulnerabilities resulting from the violation of this rule on the CERT website.

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Bibliography

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