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mem.c

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdarg.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/statfs.h>
#include "kern_util.h"
#include "user.h"
#include "mem_user.h"
#include "init.h"
#include "os.h"
#include "tempfile.h"
#include "kern_constants.h"

#include <sys/param.h>

/* Modified by which_tmpdir, which is called during early boot */
static char *default_tmpdir = "/tmp";

/*
 *  Modified when creating the physical memory file and when checking
 * the tmp filesystem for usability, both happening during early boot.
 */
static char *tempdir = NULL;

static void __init find_tempdir(void)
{
      char *dirs[] = { "TMP", "TEMP", "TMPDIR", NULL };
      int i;
      char *dir = NULL;

      if(tempdir != NULL) /* We've already been called */
            return;
      for(i = 0; dirs[i]; i++){
            dir = getenv(dirs[i]);
            if((dir != NULL) && (*dir != '\0'))
                  break;
      }
      if((dir == NULL) || (*dir == '\0'))
            dir = default_tmpdir;

      tempdir = malloc(strlen(dir) + 2);
      if(tempdir == NULL){
            fprintf(stderr, "Failed to malloc tempdir, "
                  "errno = %d\n", errno);
            return;
      }
      strcpy(tempdir, dir);
      strcat(tempdir, "/");
}

/* This will return 1, with the first character in buf being the
 * character following the next instance of c in the file.  This will
 * read the file as needed.  If there's an error, -errno is returned;
 * if the end of the file is reached, 0 is returned.
 */
static int next(int fd, char *buf, int size, char c)
{
      int n, len;
      char *ptr;

      while((ptr = strchr(buf, c)) == NULL){
            n = read(fd, buf, size - 1);
            if(n == 0)
                  return 0;
            else if(n < 0)
                  return -errno;

            buf[n] = '\0';
      }

      ptr++;
      len = strlen(ptr);
      memmove(buf, ptr, len + 1);

      /* Refill the buffer so that if there's a partial string that we care
       * about, it will be completed, and we can recognize it.
       */
      n = read(fd, &buf[len], size - len - 1);
      if(n < 0)
            return -errno;

      buf[len + n] = '\0';
      return 1;
}

/* which_tmpdir is called only during early boot */
static int checked_tmpdir = 0;

/* Look for a tmpfs mounted at /dev/shm.  I couldn't find a cleaner
 * way to do this than to parse /proc/mounts.  statfs will return the
 * same filesystem magic number and fs id for both /dev and /dev/shm
 * when they are both tmpfs, so you can't tell if they are different
 * filesystems.  Also, there seems to be no other way of finding the
 * mount point of a filesystem from within it.
 *
 * If a /dev/shm tmpfs entry is found, then we switch to using it.
 * Otherwise, we stay with the default /tmp.
 */
static void which_tmpdir(void)
{
      int fd, found;
      char buf[128] = { '\0' };

      if(checked_tmpdir)
            return;

      checked_tmpdir = 1;

      printf("Checking for tmpfs mount on /dev/shm...");

      fd = open("/proc/mounts", O_RDONLY);
      if(fd < 0){
            printf("failed to open /proc/mounts, errno = %d\n", errno);
            return;
      }

      while(1){
            found = next(fd, buf, ARRAY_SIZE(buf), ' ');
            if(found != 1)
                  break;

            if(!strncmp(buf, "/dev/shm", strlen("/dev/shm")))
                  goto found;

            found = next(fd, buf, ARRAY_SIZE(buf), '\n');
            if(found != 1)
                  break;
      }

err:
      if(found == 0)
            printf("nothing mounted on /dev/shm\n");
      else if(found < 0)
            printf("read returned errno %d\n", -found);

out:
      close(fd);

      return;

found:
      found = next(fd, buf, ARRAY_SIZE(buf), ' ');
      if(found != 1)
            goto err;

      if(strncmp(buf, "tmpfs", strlen("tmpfs"))){
            printf("not tmpfs\n");
            goto out;
      }

      printf("OK\n");
      default_tmpdir = "/dev/shm";
      goto out;
}

/*
 * This proc still used in tt-mode
 * (file: kernel/tt/ptproxy/proxy.c, proc: start_debugger).
 * So it isn't 'static' yet.
 */
int __init make_tempfile(const char *template, char **out_tempname,
                   int do_unlink)
{
      char *tempname;
      int fd;

      which_tmpdir();
      tempname = malloc(MAXPATHLEN);

      find_tempdir();
      if (template[0] != '/')
            strcpy(tempname, tempdir);
      else
            tempname[0] = '\0';
      strcat(tempname, template);
      fd = mkstemp(tempname);
      if(fd < 0){
            fprintf(stderr, "open - cannot create %s: %s\n", tempname,
                  strerror(errno));
            goto out;
      }
      if(do_unlink && (unlink(tempname) < 0)){
            perror("unlink");
            goto out;
      }
      if(out_tempname){
            *out_tempname = tempname;
      } else {
            free(tempname);
      }
      return fd;
out:
      free(tempname);
      return -1;
}

#define TEMPNAME_TEMPLATE "vm_file-XXXXXX"

/*
 * This proc is used in start_up.c
 * So it isn't 'static'.
 */
int __init create_tmp_file(unsigned long long len)
{
      int fd, err;
      char zero;

      fd = make_tempfile(TEMPNAME_TEMPLATE, NULL, 1);
      if(fd < 0) {
            exit(1);
      }

      err = fchmod(fd, 0777);
      if(err < 0){
            perror("fchmod");
            exit(1);
      }

      /* Seek to len - 1 because writing a character there will
       * increase the file size by one byte, to the desired length.
       */
      if (lseek64(fd, len - 1, SEEK_SET) < 0) {
            perror("lseek64");
            exit(1);
      }

      zero = 0;

      err = write(fd, &zero, 1);
      if(err != 1){
            perror("write");
            exit(1);
      }

      return fd;
}

int __init create_mem_file(unsigned long long len)
{
      int err, fd;

      fd = create_tmp_file(len);

      err = os_set_exec_close(fd);
      if(err < 0){
            errno = -err;
            perror("exec_close");
      }
      return fd;
}


void __init check_tmpexec(void)
{
      void *addr;
      int err, fd = create_tmp_file(UM_KERN_PAGE_SIZE);

      addr = mmap(NULL, UM_KERN_PAGE_SIZE,
                PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, fd, 0);
      printf("Checking PROT_EXEC mmap in %s...",tempdir);
      fflush(stdout);
      if(addr == MAP_FAILED){
            err = errno;
            perror("failed");
            if(err == EPERM)
                  printf("%s must be not mounted noexec\n",tempdir);
            exit(1);
      }
      printf("OK\n");
      munmap(addr, UM_KERN_PAGE_SIZE);

      close(fd);
}

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