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The only value that can be considered interchangeable between pointers and integers is the constant 0. Except in this case, conversions between integers and pointers may have undesired consequences depending on the [implementation|BB. Definitions#implementation]. According to C99 \[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\]: |
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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These issues arise because the mapping functions for converting a pointer to an integer or an integer to a pointer must be consistent with the addressing structure of the execution environment. For example, not all machines have a flat memory model.
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In this noncompliant code example, the pointer ptr is converted to an integer value. Both a pointer and an int are assumed to be 32 bits. The high-order 9 bits of the number are used to hold a flag value, and the result is converted back into a pointer.
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Please note that this noncompliant code example also violates guideline EXP11-C. Do not apply operators expecting one type to data of an incompatible type.
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Saving a few bits of storage is generally not as important as writing portable code. A struct can be used to provide room for both the pointer and the flag value. This is portable to machines of different word sizes, both smaller and larger than 32 bits, and works working even when pointers cannot be represented in any integer type.
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Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
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INT11-C | low | probable | high | P2 | L3 |
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Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Other Languages
Related Guidelines
This rule appears in the C++ Secure Coding Standard as : INT11-CPP. Take care when converting from pointer to integer or integer to pointer.
Bibliography
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\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.3.2.3, "Pointers" \[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "HFC Pointer casting and pointer type changes" \[[MITRE 072007|AA. Bibliography#MITRE 07]\] [CWE ID 466|http://cwe.mitre.org/data/definitions/466.html], "Return of Pointer Value Outside of Expected Range," and [CWE ID 587|http://cwe.mitre.org/data/definitions/587.html], "Assignment of a Fixed Address to a Pointer" |
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