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Conversions between integers and pointers can have undesired consequences depending on the implementation.

According to the to the C Standard, subclause 6.3.2.3 3 [ISO/IEC 9899:20112024],

An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might be a trap representation.

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The result of this assignment is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might be a trap representation.

Compliant Solution

Adding an explicit cast may help the compiler convert the integer value into a valid pointer. A common technique is to assign the integer to a volatile-qualified object of type intptr_t or uintptr_t and then assign the integer value to the pointer:

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Unfortunately this code cannot be made safe while strictly conforming to ISO C.

A particular platform (that is, hardware, operating system, compiler, and Standard C library) might guarantee that a memory address is correctly aligned for the pointer type, and actually contains a value for that type. A common practice is to use addresses that are known to point to hardware that provides valid values.

Exceptions

INT36-C-EX1: A null pointer can be converted to an integer; it takes on the value 0. Likewise, the integer value 0  The integer value 0 can be converted to a pointer; it becomes the null pointer.

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Related Vulnerabilities

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

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Bibliography

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