memcpy_s() and memmove_s()

Development Context

Copying characters from one memory location to another.

Technology Context

C++, C, UNIX, Win32

Attacks

Attacker executes arbitrary code on machine with permissions of compromised process or changes the behavior of the program.

Risk

The memcpy() and  memmove() functions are a source of buffer overflow vulnerabilities.

Description

The memcpy_s() and memmove_s() functions defined in ISO/IEC TR 24731 are similar to the corresponding less-secure memcpy() and memmove() functions but provide some additional safeguards. The secure versions of these functions add an additional argument that specifies the maximum size of the destination. The memcpy_s() and memmove_s() functions return zero if successful. A nonzero value is returned if either the source or desti­nation pointer is NULL, if the specified number of characters to copy/move is greater than the maximum size of the destination buffer, or the number of charac­ters to copy/move or the maximum size of the destination buffer is greater than RSIZE_MAX.1

References

• 1. The RSIZE_MAX is used to limit the size of objects passed to functions that have parameters of type rsize_t . 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. Also, some implementations do not support objects as large as the maximum value that can be represented by type size_t . As a result, it is sometimes beneficial to restrict the range of object sizes to detect potential vulnerabilities.