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The signature is similar to strcpy() but takes an extra argument of type rsize_t that specifies the maximum length of the destination buffer. ( Functions that accept parameters of type rsize_t diagnose a constraint violation, if the values of those parameters are greater than RSIZE_MAX. Extremely large object sizes are frequently a sign that an object's size was calculated incorrectly. For example, negative numbers appear as very large positive numbers when converted to an unsigned type like size_t. For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect errors. For machines with large address spaces, ISO/IEC TR 24731-1 recommends that RSIZE_MAX be defined as the smaller of the size of the largest object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of some legitimate, but very large, objects. See also guideline recommendation INT01-C. Use rsize_t or size_t for all integer values representing the size of an object.
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When a runtime-constraint violation is detected, the destination string is set to the null string (as long as it is not a null pointer, and the maximum length of the destination buffer is greater than zero and not greater than RSIZE_MAX) and the function returns a nonzero value. In the following example, the strcpy_s() function is used to copy src1 to dst1.
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ISO/IEC TR 24731-1 functions are still capable of overflowing a buffer if the maximum length of the destination buffer and number of characters to copy are incorrectly specified. ISO/IEC TR 24731-2 functions may can make it more difficult to keep track of memory that must be freed, leading to memory leaks. As a result, the ISO/IEC TR 24731 functions are not particularly secure but may be useful in preventive maintenance to reduce the likelihood of vulnerabilities in an existing legacy code base.
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The following compliant solution performs some of the checking at compile time using a static assertion. (See guideline recommendation DCL03-C. Use a static assertion to test the value of a constant expression.)
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Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Bibliography
Related Guidelines
Wiki Markup
ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] TR 24772 "TRJ Use of Libraries" \[[
Bibliography
| Wiki Markup |
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|AA. Bibliography#ISO/IEC TR 24731-1-2007]\]
\[[Seacord 2005a|AA. Bibliography#Seacord 05a]\] Chapter 2, "Strings"
\[[Seacord 2005b|AA. Bibliography#Seacord 05b]\] |
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