Fix NULL pointer dereference in freenect_init_registration_table()

[hirorogo]

Summary

In freenect_init_registration_table() (src/registration.c), two malloc() calls allocate temporary buffers that are immediately passed to memset() and later used for array indexing without NULL checks. If either allocation fails, this causes a NULL pointer dereference. Added a guard clause after both allocations.

PoC

// Reproduction: freenect_init_registration_table NULL dereference
// malloc failure -> memset(NULL, ...) -> crash
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Simulates the buggy init function
int init_registration_table_buggy(int num_pixels) {
    double *reg_pad = (double *)malloc(num_pixels * sizeof(double));
    double *reg_dist = (double *)malloc(num_pixels * sizeof(double));

    // BUG: no NULL check — crashes if malloc returns NULL
    memset(reg_pad, 0, num_pixels * sizeof(double));   // NULL deref
    memset(reg_dist, 0, num_pixels * sizeof(double));   // NULL deref

    // ... array access reg_pad[i], reg_dist[i] ...
    free(reg_pad);
    free(reg_dist);
    return 0;
}

int init_registration_table_fixed(int num_pixels) {
    double *reg_pad = (double *)malloc(num_pixels * sizeof(double));
    double *reg_dist = (double *)malloc(num_pixels * sizeof(double));

    // FIX: NULL check
    if (!reg_pad || !reg_dist) {
        printf("  FIXED: allocation failed, returning safely\n");
        free(reg_pad);
        free(reg_dist);
        return -1;
    }

    memset(reg_pad, 0, num_pixels * sizeof(double));
    memset(reg_dist, 0, num_pixels * sizeof(double));
    free(reg_pad);
    free(reg_dist);
    return 0;
}

int main() {
    // Force malloc failure by requesting absurd size
    size_t huge = (size_t)-1 / 2;

    printf("=== FIXED ===\n");
    init_registration_table_fixed(huge);

    printf("=== BUGGY ===\n");
#ifdef _WIN32
    __try {
        init_registration_table_buggy(huge);
    } __except(1) {
        printf("  ACCESS VIOLATION: NULL pointer dereference confirmed\n");
    }
#endif
    return 0;
}

Output:

=== FIXED ===
  FIXED: allocation failed, returning safely
=== BUGGY ===
  ACCESS VIOLATION: NULL pointer dereference confirmed

Test plan

• Project builds successfully with the change
• No functional regression in registration table initialization