Heap Overflow

Alice wrote a heap management library, and she uses the following data structures to manage heap: struct heap_sector { int size; // size of the heap sector char *sector; // pointer to the first char struct heap_sector *prev; // pointer to previous sector struct heap_sector *next; // pointer to next sector }; struct heap_sector *heap_free; // pointer to the list of free heap memory struct heap_sector *heap_used; // pointer to the list of used heap memory And use the following logic to manage memory: • heap used is initialized as NULL, and heap free is initialised to the first available byte; • malloc(int n) function always allocates the first a few memory sectors whose size is larger than sizeof(struct heap sector) + 1 (until the total size equals to n) to user process, and moves the memory from heap free to heap used; if there is no enough space to allocate, it returns NULL; • free(char* h) will free the corresponding heap and move the memory from heap used to heap free. Answer the following questions: Please write the pseudo code for malloc(int n) and free(char* h); • The design is potentially vulnerable to integer overflow. Please explain how this may happen, and how your pseudo code avoids this problem. • The design is potentially vulnerable to heap overflow. Please explain how it may happen and how your pseudo code avoids such problems. • The design is potentially vulnerable to off-by-one attack. Please explain how this attack may happen and how your pseudo code avoids such problems. • The design is potentially vulnerable to TOCTTOU problem. Please explain how it may happen and how your design avoids such problems. • Users may free the allocated memory twice or multiple times. Please explain how your design can prevent this.