![]() Now lets try it wirh GDB to get a better understanding. – 8 bytes of buf variable is stored in the stack and 4 bytes of the old EBP is stored. – Once the execution goes to the input(), old value of the EBP will be stored and then local variables will be pushed into the stack. – When main() program transfers control to the input() function, it will push the next instruction ie ‘return 0’ on to the stack. – Input() functions is not taking any argument, thus there are no arguments which are pushed into the stack. Vulnerable program stack layout: Vulnerable program stack layout Let’s analyse the source code to understand further. So when executed, the program will throw “Segmentation fault (core dumped)”. Observe that the given string is “SecPod SecPod”, which is more than the size of the buffer available. Now, go ahead run the program with large data input. Here, we had given the input string “SecPod” which is less than the size of the buffer, so the program will print the string “SecPod” and exits normally. Lets go ahead and run the the program with normal size of the buffer. ![]() Suppose, if user supplies more than 8 bytes of data and gets() will still happily go ahead and write that onto the memory. In the above code gets() is used which is going to get input from the user and writes into the variable ‘buf’ without checking the size of the variable ‘buf’. Gets(buf) / gets() itself is dangerous function because it does not do the bound check./ Let’s consider some sample code which is vulnerable to stack based buffer overflow. Generally, heap overflow will happen in the heap area when allocating the memory dynamically using runtime memory allocation techniques. – Overwriting a parameter of a different stack frame or a nonlocal address. It is due to an improper bound checking and results in overwriting the adjacent memory locations. POP: Remove the data from the stack.(After remove fix ESP to top of the stack)īuffer overflow occurs when the larger data is written to the buffer without checking the actual size of the buffer. Stack is LIFO data structure, that is Last in First Out. Anything which is put into the stack last is the first which will have to be removed. Stack always grows down the memory address, from higher to lower and ESP points to the top of the stack. – Uninitialized data segment (BSS): Contains uninitialized data.Ĭode or Text : Contains actual executable code or executable instructions. – Initialized data segment: Contains the global, static and constant data. Heap: Contains the dynamically allocated memory (malloc()). Stack: Contains arguments which are passed to the function and local variables. ![]() In general, the term buffer is a temporary storage, a space in the memory used to store the data. ![]()
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