Memory Model & Pointer Problems

Text (Code)

machine instructions, read-only, entire program lifetime

Data

initialized globals/statics (int x = 5; at global scope)

BSS

uninitialized globals/statics, auto-zeroed by OS

Heap

dynamic allocation (malloc/new), grows upward, you manage lifetime

Stack

local vars + function args, grows downward, auto-managed

Dangling Pointer

A pointer that points to memory that has already been freed. Accessing it is undefined behavior and a security risk.

Lost Heap Variable (Memory Leak)

A heap allocation that can no longer be reached — no pointer points to it. Cannot be freed. Accumulates = memory leak.

Array Out of Bounds

Out-of-bounds writes are the root cause of buffer overflow attacks.

Unchecked open()

returns -1 on failure. Must check before using fd.

Unchecked read()

read() returns bytes read. Negative = error. Fewer bytes = partial read.

Invalid len to malloc

If len is negative or too large, conversion to unsigned size_t can cause a huge/incorrect allocation request.

Unchecked malloc()

malloc() returns NULL on failure. Must check before dereferencing.

Missing null terminator

Allocating len bytes for a string but needing len+1 for '\0'.

Missing free()/close()

Not freeing memory or closing file descriptors = resource leaks.