Security Pattern: Systematic NULL Pointer Vulnerabilities

[smooge]

Priority: HIGH
File: Src/checkX.c
Function: Multiple functions (user_exists, check_lock, canseelogin)
Discovered: During systematic security pattern analysis

Description: Multiple functions in checkX.c lack NULL pointer validation, creating a pattern of vulnerability.

Functions Affected:

• user_exists(): No NULL check before getpwnam(who)
• check_lock(): No NULL check before open(filename, ...)
• canseelogin(): No NULL check before strcmp(loginname, ...)

Impact: Systematic crashes when NULL pointers are passed to these security-critical functions.

Proposed Fix: Implement systematic NULL checks across all checkX.c functions:

/* Pattern for all functions */
if (parameter == NULL) {
    return appropriate_error_value;
}

Original Bug ID: BUG-006