Rewriting ret address when leaving a function - c

Question

I'm trying to rewrite ret adress from function foo() to skip first instruction after leaving function foo(). I'm following Smash stack for fun or profit and Hacking by Jon Erickson. Here is simple code where I want to skip "b = 2;" instruction, so in b should be stored value 1.
Compiled in gcc, settings: -fno-stack-protector -z execstack -g
Also I have turned off ASLR.
#include <stdio.h>
int foo() {
int c = 0;
int *ptr;
ptr = (int*) 0x00007fffffffdf38;
// Second instruction after leaving from foo(). I also tried to skip all instructions before call printf function.
*ptr = 0x0000000000400577;
return 0;
}
int main()
{
int b = 1;
foo();
b = 2;
printf("b = %d\n", b);
return 0;
}
Output of this program is: "b = 2".
How I assumed where is stored RET instruction:
(gdb) disass main
...
0x000000000040056b <+20>: call 0x40052d <foo>
0x0000000000400570 <+25>: mov DWORD PTR [rbp-0x4],0x2
0x0000000000400577 <+32>: mov eax,DWORD PTR [rbp-0x4]
0x000000000040057a <+35>: mov esi,eax
...
(gdb) break 4 // set breakpoint 1 in function foo before int *ptr;
(gdb) break 7 // set breakpoint 2 in function foo after rewriting RET for checking
(gdb) run
(gdb) x/8x &c // "x/8x $esp" doesn't work, it says: "Cannot access memory at address 0xffffffffffffdf30", so I'm looking into memory from &c
0x7fffffffdf2c: 0x00000000 0xffffdf50 0x00007fff 0x00400570
0x7fffffffdf3c: 0x00000000 0xffffe030 0x00007fff 0x00000000
// simple math tell me, it should be:
(gdb) x/8xb 0x7fffffffdf38
0x7fffffffdf38: 0x70 0x05 0x40 0x00 0x00 0x00 0x00 0x00
This is how I have found the RET address, it is at 0x7fffffffdf38. To this place I'm putting address of next instruction - 0x0000000000400577.
However, computer still didn't skip instruction b = 2, even when RET is successfully rewrited.
I checked it for confirmation if it really replaced the RET address:
(gdb) c
(gdb) x/8xb 0x7fffffffdf38
0x7fffffffdf38: 0x77 0x05 0x40 0x00 0x00 0x00 0x00 0x00
So RET address is really rewrited but when program leaves from function foo() it jumps to original address 0x0000000000400570 wich I want to skip...
It should be simple, find where is stored ret adress and then put to this place other adress. What am I doing wrong?
Thanks for every answer.
For specifying the questing I'm adding dissasembled functions:
Dump of assembler code for function foo:
0x000000000040052d <+0>: push rbp
0x000000000040052e <+1>: mov rbp,rsp
0x0000000000400531 <+4>: mov DWORD PTR [rbp-0x4],0x0
0x0000000000400538 <+11>: movabs rax,0x7fffffffdf38
0x0000000000400542 <+21>: mov QWORD PTR [rbp-0x10],rax
0x0000000000400546 <+25>: mov rax,QWORD PTR [rbp-0x10]
0x000000000040054a <+29>: mov DWORD PTR [rax],0x400577
0x0000000000400550 <+35>: mov eax,0x0
0x0000000000400555 <+40>: pop rbp
0x0000000000400556 <+41>: ret
End of assembler dump.
(gdb) disass main
Dump of assembler code for function main:
0x0000000000400557 <+0>: push rbp
0x0000000000400558 <+1>: mov rbp,rsp
0x000000000040055b <+4>: sub rsp,0x10
0x000000000040055f <+8>: mov DWORD PTR [rbp-0x4],0x1
0x0000000000400566 <+15>: mov eax,0x0
0x000000000040056b <+20>: call 0x40052d <foo>
0x0000000000400570 <+25>: mov DWORD PTR [rbp-0x4],0x2
0x0000000000400577 <+32>: mov eax,DWORD PTR [rbp-0x4]
0x000000000040057a <+35>: mov esi,eax
0x000000000040057c <+37>: mov edi,0x400624
0x0000000000400581 <+42>: mov eax,0x0
0x0000000000400586 <+47>: call 0x400410 <printf#plt>
0x000000000040058b <+52>: mov eax,0x0
0x0000000000400590 <+57>: leave
0x0000000000400591 <+58>: ret

Answer 1

When I run this in gdb debugger it works. So the code is written good, question solved. The problem is somewhere else...