## Buffer Overflow Analysis Method

For buffer overflow analysis, you must start from the Sink point and clarify three things:

- Whether the read/write content is externally controllable
- The buffer length L_buffer
- The allowed read/write length L_allow

Both the buffer length and whether the content is externally controllable can be determined by tracing the data flow. Below, the focus is on how to analyze the allowed read/write length L_allow.

- First, check whether the Sink point function has a read/write length parameter. If it does, trace the data flow to analyze the source of the parameter variable, and analyze the possible ratio of this parameter to the buffer length L_buffer (unknown length = N times). This parameter is L_allow.
- If there is no read/write length parameter limit, then the actual allowed read/write length is the length of the read/write content variable (denoted as L_content).
  - Next, focus on the read/write content length. First, map out the data flow and identify all code that may limit the read/write content length before reaching the Sink point (distinguish between code that merely uses length calculations and code that performs validation/restriction).
  - Analyze each limiting code to determine how many times L_content may exceed the buffer length L_buffer (unknown length = N times). The smallest value is L_allow.
  - Note: Code that calculates length must account for **integer overflow** issues.

Finally, compare L_allow and L_buffer. If it is possible that L_allow > L_buffer, a buffer overflow exists; otherwise, it does not.

## Analysis Notes

- Some code uses read/write content length calculations but does not produce a limiting effect. These must be strictly distinguished.
- You must explicitly list the possible size of L_allow and compare it with L_buffer.
- If the length restriction involves mathematical operations (addition, subtraction, multiplication, division, etc.), you must additionally consider **integer underflow** issues (because read/write lengths are typically unsigned integers, and negative numbers would be implicitly converted to very large positive numbers, causing out-of-bounds read/write).
