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    Subjectnet/llc: bug in llc_pdu_init_as_xid_cmd/skb_over_panic
    Hi,

    I've got the following error report while fuzzing the kernel with syzkaller.

    On commit 926af6273fc683cd98cd0ce7bf0d04a02eed6742.

    A reproducer and .config are attached

    kernel BUG at net/core/skbuff.c:105!
    invalid opcode: 0000 [#1] SMP KASAN
    Dumping ftrace buffer:
    (ftrace buffer empty)
    Modules linked in:
    CPU: 2 PID: 6558 Comm: syz-executor4 Not tainted 4.10.0-rc7+ #126
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
    task: ffff88003c49c480 task.stack: ffff88003a5c0000
    RIP: 0010:skb_panic+0x16f/0x200 net/core/skbuff.c:101
    RSP: 0018:ffff88003a5c77d0 EFLAGS: 00010286
    RAX: 0000000000000082 RBX: ffff88006be991c0 RCX: 0000000000000000
    RDX: 0000000000000082 RSI: ffffffff814567fc RDI: ffffed00074b8eec
    RBP: ffff88003a5c7838 R08: 0000000000000001 R09: 0000000000000000
    R10: 0000000000000002 R11: 0000000000000001 R12: ffffffff85231ee0
    R13: ffffffff834a6722 R14: 0000000000000003 R15: ffff88006c81c580
    FS: 00007f89298c7700(0000) GS:ffff88006de00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000020ee5000 CR3: 0000000058697000 CR4: 00000000000006e0
    Call Trace:
    skb_over_panic net/core/skbuff.c:110 [inline]
    skb_put+0x18d/0x1d0 net/core/skbuff.c:1437
    llc_pdu_init_as_xid_cmd include/net/llc_pdu.h:377 [inline]
    llc_sap_action_send_xid_c+0x2a2/0x3b0 net/llc/llc_s_ac.c:82
    llc_exec_sap_trans_actions net/llc/llc_sap.c:152 [inline]
    llc_sap_next_state net/llc/llc_sap.c:181 [inline]
    llc_sap_state_process+0x26b/0x4e0 net/llc/llc_sap.c:212
    llc_build_and_send_xid_pkt+0x19f/0x200 net/llc/llc_sap.c:276
    llc_ui_sendmsg+0xad9/0x1430 net/llc/af_llc.c:938
    sock_sendmsg_nosec net/socket.c:635 [inline]
    sock_sendmsg+0xca/0x110 net/socket.c:645
    ___sys_sendmsg+0x9d2/0xae0 net/socket.c:1985
    __sys_sendmsg+0x138/0x320 net/socket.c:2019
    SYSC_sendmsg net/socket.c:2030 [inline]
    SyS_sendmsg+0x2d/0x50 net/socket.c:2026
    entry_SYSCALL_64_fastpath+0x1f/0xc2
    RIP: 0033:0x4458b9
    RSP: 002b:00007f89298c6b58 EFLAGS: 00000286 ORIG_RAX: 000000000000002e
    RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00000000004458b9
    RDX: 0000000000040085 RSI: 0000000020001fc8 RDI: 0000000000000005
    RBP: 00000000006e1ae0 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000708000
    R13: ffffffffffffffff R14: 00000000c0206434 R15: 00000000201fcfe0
    Code: 00 00 00 48 89 54 24 10 48 c7 c7 60 19 23 85 48 89 74 24 08 4c
    89 04 24 4c 89 ea 4c 89 7c 24 18 45 89 f0 4c 89 e6 e8 1e c0 38 fe <0f>
    0b 4c 89 4d b8 4c 89 45 c0 48 89 75 c8 48 89 55 d0 e8 6a 5e
    RIP: skb_panic+0x16f/0x200 net/core/skbuff.c:101 RSP: ffff88003a5c77d0
    ---[ end trace 89f0ca2ea5bc3ead ]---
    Kernel panic - not syncing: Fatal exception
    Dumping ftrace buffer:
    (ftrace buffer empty)
    Kernel Offset: disabled
    Rebooting in 86400 seconds..
    [unhandled content-type:application/octet-stream]// autogenerated by syzkaller (http://github.com/google/syzkaller)

    #ifndef __NR_mmap
    #define __NR_mmap 9
    #endif
    #ifndef __NR_socket
    #define __NR_socket 41
    #endif
    #ifndef __NR_sendmsg
    #define __NR_sendmsg 46
    #endif

    #define _GNU_SOURCE

    #include <sys/ioctl.h>
    #include <sys/mman.h>
    #include <sys/mount.h>
    #include <sys/prctl.h>
    #include <sys/resource.h>
    #include <sys/socket.h>
    #include <sys/stat.h>
    #include <sys/syscall.h>
    #include <sys/time.h>
    #include <sys/types.h>
    #include <sys/wait.h>

    #include <linux/capability.h>
    #include <linux/if.h>
    #include <linux/if_tun.h>
    #include <linux/kvm.h>
    #include <linux/sched.h>
    #include <net/if_arp.h>

    #include <assert.h>
    #include <dirent.h>
    #include <errno.h>
    #include <fcntl.h>
    #include <grp.h>
    #include <pthread.h>
    #include <setjmp.h>
    #include <signal.h>
    #include <stdarg.h>
    #include <stdbool.h>
    #include <stddef.h>
    #include <stdint.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>

    const int kFailStatus = 67;
    const int kErrorStatus = 68;
    const int kRetryStatus = 69;

    __attribute__((noreturn)) void doexit(int status)
    {
    volatile unsigned i;
    syscall(__NR_exit_group, status);
    for (i = 0;; i++) {
    }
    }

    __attribute__((noreturn)) void fail(const char* msg, ...)
    {
    int e = errno;
    fflush(stdout);
    va_list args;
    va_start(args, msg);
    vfprintf(stderr, msg, args);
    va_end(args);
    fprintf(stderr, " (errno %d)\n", e);
    doexit(e == ENOMEM ? kRetryStatus : kFailStatus);
    }

    __attribute__((noreturn)) void exitf(const char* msg, ...)
    {
    int e = errno;
    fflush(stdout);
    va_list args;
    va_start(args, msg);
    vfprintf(stderr, msg, args);
    va_end(args);
    fprintf(stderr, " (errno %d)\n", e);
    doexit(kRetryStatus);
    }

    static int flag_debug;

    void debug(const char* msg, ...)
    {
    if (!flag_debug)
    return;
    va_list args;
    va_start(args, msg);
    vfprintf(stdout, msg, args);
    va_end(args);
    fflush(stdout);
    }

    __thread int skip_segv;
    __thread jmp_buf segv_env;

    static void segv_handler(int sig, siginfo_t* info, void* uctx)
    {
    uintptr_t addr = (uintptr_t)info->si_addr;
    const uintptr_t prog_start = 1 << 20;
    const uintptr_t prog_end = 100 << 20;
    if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED) &&
    (addr < prog_start || addr > prog_end)) {
    debug("SIGSEGV on %p, skipping\n", addr);
    _longjmp(segv_env, 1);
    }
    debug("SIGSEGV on %p, exiting\n", addr);
    doexit(sig);
    for (;;) {
    }
    }

    static void install_segv_handler()
    {
    struct sigaction sa;
    memset(&sa, 0, sizeof(sa));
    sa.sa_sigaction = segv_handler;
    sa.sa_flags = SA_NODEFER | SA_SIGINFO;
    sigaction(SIGSEGV, &sa, NULL);
    sigaction(SIGBUS, &sa, NULL);
    }

    #define NONFAILING(...) \
    { \
    __atomic_fetch_add(&skip_segv, 1, __ATOMIC_SEQ_CST); \
    if (_setjmp(segv_env) == 0) { \
    __VA_ARGS__; \
    } \
    __atomic_fetch_sub(&skip_segv, 1, __ATOMIC_SEQ_CST); \
    }

    #define BITMASK_LEN(type, bf_len) (type)((1ull << (bf_len)) - 1)

    #define BITMASK_LEN_OFF(type, bf_off, bf_len) \
    (type)(BITMASK_LEN(type, (bf_len)) << (bf_off))

    #define STORE_BY_BITMASK(type, addr, val, bf_off, bf_len) \
    if ((bf_off) == 0 && (bf_len) == 0) { \
    *(type*)(addr) = (type)(val); \
    } else { \
    type new_val = *(type*)(addr); \
    new_val &= ~BITMASK_LEN_OFF(type, (bf_off), (bf_len)); \
    new_val |= ((type)(val)&BITMASK_LEN(type, (bf_len))) << (bf_off); \
    *(type*)(addr) = new_val; \
    }

    static uintptr_t execute_syscall(int nr, uintptr_t a0, uintptr_t a1,
    uintptr_t a2, uintptr_t a3,
    uintptr_t a4, uintptr_t a5,
    uintptr_t a6, uintptr_t a7,
    uintptr_t a8)
    {
    switch (nr) {
    default:
    return syscall(nr, a0, a1, a2, a3, a4, a5);
    }
    }

    static void setup_main_process()
    {
    struct sigaction sa;
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = SIG_IGN;
    syscall(SYS_rt_sigaction, 0x20, &sa, NULL, 8);
    syscall(SYS_rt_sigaction, 0x21, &sa, NULL, 8);
    install_segv_handler();

    char tmpdir_template[] = "./syzkaller.XXXXXX";
    char* tmpdir = mkdtemp(tmpdir_template);
    if (!tmpdir)
    fail("failed to mkdtemp");
    if (chmod(tmpdir, 0777))
    fail("failed to chmod");
    if (chdir(tmpdir))
    fail("failed to chdir");
    }

    static void loop();

    static void sandbox_common()
    {
    prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
    setpgrp();
    setsid();

    struct rlimit rlim;
    rlim.rlim_cur = rlim.rlim_max = 128 << 20;
    setrlimit(RLIMIT_AS, &rlim);
    rlim.rlim_cur = rlim.rlim_max = 1 << 20;
    setrlimit(RLIMIT_FSIZE, &rlim);
    rlim.rlim_cur = rlim.rlim_max = 1 << 20;
    setrlimit(RLIMIT_STACK, &rlim);
    rlim.rlim_cur = rlim.rlim_max = 0;
    setrlimit(RLIMIT_CORE, &rlim);

    unshare(CLONE_NEWNS);
    unshare(CLONE_NEWIPC);
    unshare(CLONE_IO);
    }

    static int do_sandbox_none(int executor_pid, bool enable_tun)
    {
    int pid = fork();
    if (pid)
    return pid;

    sandbox_common();

    loop();
    doexit(1);
    }

    long r[24];
    void loop()
    {
    memset(r, -1, sizeof(r));
    r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0x851000ul, 0x3ul,
    0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
    r[1] = execute_syscall(__NR_socket, 0x1aul, 0x801ul, 0xcb00ul, 0, 0,
    0, 0, 0, 0);
    NONFAILING(*(uint64_t*)0x20001fc8 = (uint64_t)0x20004fa0);
    NONFAILING(*(uint32_t*)0x20001fd0 = (uint32_t)0x60);
    NONFAILING(*(uint64_t*)0x20001fd8 = (uint64_t)0x20003000);
    NONFAILING(*(uint64_t*)0x20001fe0 = (uint64_t)0x1);
    NONFAILING(*(uint64_t*)0x20001fe8 = (uint64_t)0x20001000);
    NONFAILING(*(uint64_t*)0x20001ff0 = (uint64_t)0x10);
    NONFAILING(*(uint32_t*)0x20001ff8 = (uint32_t)0x1);
    NONFAILING(*(uint16_t*)0x20004fa0 = (uint16_t)0x27);
    NONFAILING(*(uint32_t*)0x20004fa4 = (uint32_t)0x800);
    NONFAILING(*(uint32_t*)0x20004fa8 = (uint32_t)0x0);
    NONFAILING(*(uint32_t*)0x20004fac = (uint32_t)0x0);
    NONFAILING(*(uint8_t*)0x20004fb0 = (uint8_t)0xfffffffffffffffd);
    NONFAILING(*(uint8_t*)0x20004fb1 = (uint8_t)0x0);
    NONFAILING(memcpy(
    (void*)0x20004fb2,
    "\x4e\xa6\xf0\xe3\x26\x38\x41\x00\x04\xc3\x84\x5a\xd3\xe8\x12\x92"
    "\xe2\x97\x1a\x49\xc7\x07\x55\xb5\xa2\x0c\x91\x5b\xe8\xe3\xa2\x1e"
    "\x49\x17\x62\x02\x27\x36\xcd\x99\x61\x46\xb6\xa2\xa9\x9e\xfe\x01"
    "\xc9\xcb\xf2\xeb\x94\x94\x94\xc2\x85\x56\x30\xea\x2a\x71\xf9",
    63));
    NONFAILING(*(uint64_t*)0x20004ff8 = (uint64_t)0x0);
    NONFAILING(*(uint64_t*)0x20003000 = (uint64_t)0x20002000);
    NONFAILING(*(uint64_t*)0x20003008 = (uint64_t)0xa7);
    NONFAILING(memcpy(
    (void*)0x20002000,
    "\x95\x45\x2e\xff\xe1\xb2\xde\xa2\x07\xc7\x4b\xbe\x1d\x19\xd1\x1c"
    "\x25\x40\x57\x3d\x31\xa0\xfa\xc5\xaf\xcc\x44\x1d\x21\xaa\x09\xc4"
    "\x62\x54\xb9\x46\xcc\x12\x0f\x41\xcc\x99\x90\x8a\x8b\x6e\x1a\x41"
    "\x27\xfa\x11\xc5\x6c\x68\xdb\xe6\xbc\x4f\x68\x6e\x8b\xe6\xfe\x9e"
    "\xcd\x87\xd9\x7b\x82\xf9\x0d\x28\x3f\xe7\x2a\x69\xc9\x9d\x38\x7c"
    "\xcf\x30\x18\xb3\x7a\x2f\xcc\x84\xc2\x0b\x68\x7d\x77\x78\x2a\xd1"
    "\xe2\x13\xf6\x64\x89\x5e\x8f\x98\xab\x5c\xce\x7f\xfa\xae\x77\x1c"
    "\x14\x41\xb8\x2d\x30\x3a\x0f\x36\x06\x52\x4f\x9f\xdf\x44\xd8\x32"
    "\x6b\x28\x91\xde\xa3\x8f\x94\x47\x77\xb0\x1d\xf2\x74\x75\xc5\x53"
    "\xa4\x1f\x3f\xba\x7b\x0d\x57\xae\xd6\xfb\x0f\xb1\xbb\xfd\x47\x61"
    "\x36\x7a\x1d\x9e\xda\x18\x48",
    167));
    NONFAILING(*(uint64_t*)0x20001000 = (uint64_t)0x10);
    NONFAILING(*(uint32_t*)0x20001008 = (uint32_t)0x1);
    NONFAILING(*(uint32_t*)0x2000100c = (uint32_t)0x2);
    r[23] = execute_syscall(__NR_sendmsg, r[1], 0x20001fc8ul, 0x40085ul,
    0, 0, 0, 0, 0, 0);
    }
    int main()
    {
    setup_main_process();
    int pid = do_sandbox_none(0, false);
    int status = 0;
    while (waitpid(pid, &status, __WALL) != pid) {
    }
    return 0;
    }
    \
     
     \ /
      Last update: 2017-02-10 16:40    [W:7.336 / U:0.100 seconds]
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