Strings (both character and wide-character) are often subject to buffer overflows, which will overwrite the memory immediately past the string. Many rules warn against buffer overflows, including STR31-C. Guarantee that storage for strings has sufficient space for character data and the null terminator. Sometimes the danger of buffer overflows can be minimized by ensuring that arranging memory such that data that might be corrupted by a buffer overflow is not sensitive.
Noncompliant Code Example
This noncompliant code example stores a set of strings using a linked list:
A buffer overflow on
name would overwrite the
next pointer, which could then be used to read or write to arbitrary memory.
This compliant solution creates a linked list of strings but stores the
next pointer before the string:
If buffer overflow occurs on
next pointer remains uncorrupted.
In this compliant solution, the linked list stores pointers to strings that are stored elsewhere. Storing the strings elsewhere protects the
next pointer from buffer overflows on the strings.
API01-C-EX1: Using a string before sensitive data such as pointers is permitted when it is not practical to segregate the strings from the sensitive data.
Each of the following code examples creates a linked list of strings, but each node is actually stored inside an array. This practice ensures that the string is always in front of a
next pointer regardless of how they are ordered in the struct.
Failure to follow this recommendation can result in memory corruption from buffer overflows, which can easily corrupt data or yield remote code execution.
Avoid overflow when writing to a buffer