Page History

...

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 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.) The semantics are also similar. When there are no input validation errors, the strcpy_s() function copies characters from a source string to a destination character array up to and including the terminating null NULL character. The function returns zero on success.

...

• The source and destination pointers are checked to see if they are nullNULL.
• The maximum length of the destination buffer is checked to see if it is equal to zero, greater than RSIZE_MAX, or less than or equal to the length of the source string.

When a constraint violation is detected, the destination string is set to the null NULL string and the function returns a nonzero value. In the following example, the strcpy_s() function is used to copy src1 to dst1.

...

Users of the ISO/IEC TR 24731 functions are less likely to introduce a security flaw because the size of the destination buffer and the maximum number of characters to append must be specified. ISO/IEC TR 24731 functions also ensure null NULL termination of the destination string.

...

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

References

\[[ISO/IEC TR 24731-2006|AA. C References#ISO/IEC TR 24731-2006]\]
\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 7.21, "String handling <string.h>"
\[[Seacord 05a|AA. C References#Seacord 05a]\] Chapter 2, "Strings"
\[[Seacord 05b|AA. C References#Seacord 05b]\]