unix/syslinux.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 1998-2007 H. Peter Anvin - All Rights Reserved
   4  *
   5  *   This program is free software; you can redistribute it and/or modify
   6  *   it under the terms of the GNU General Public License as published by
   7  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   8  *   Boston MA 02111-1307, USA; either version 2 of the License, or
   9  *   (at your option) any later version; incorporated herein by reference.
  10  *
  11  * ----------------------------------------------------------------------- */
  12
  13 /*
  14  * syslinux.c - Linux installer program for SYSLINUX
  15  *
  16  * This program ought to be portable.  I hope so, at least.
  17  *
  18  * This is an alternate version of the installer which doesn't require
  19  * mtools, but requires root privilege.
  20  */
  21
  22 /*
  23  * If DO_DIRECT_MOUNT is 0, call mount(8)
  24  * If DO_DIRECT_MOUNT is 1, call mount(2)
  25  */
  26 #ifdef __KLIBC__
  27 # define DO_DIRECT_MOUNT 1
  28 #else
  29 # define DO_DIRECT_MOUNT 0      /* glibc has broken losetup ioctls */
  30 #endif
  31
  32 #define _GNU_SOURCE
  33 #define _XOPEN_SOURCE 500       /* For pread() pwrite() */
  34 #define _FILE_OFFSET_BITS 64
  35 #include <alloca.h>
  36 #include <errno.h>
  37 #include <fcntl.h>
  38 #include <paths.h>
  39 #include <stdio.h>
  40 #include <string.h>
  41 #include <stdlib.h>
  42 #include <unistd.h>
  43 #include <inttypes.h>
  44 #include <sys/stat.h>
  45 #include <sys/types.h>
  46 #include <sys/wait.h>
  47 #include <sys/mount.h>
  48
  49 #include "syslinux.h"
  50 #include "libfat.h"
  51
  52 #if DO_DIRECT_MOUNT
  53
  54 # include <linux/loop.h>
  55
  56 #else
  57
  58 # include <paths.h>
  59 # ifndef _PATH_MOUNT
  60 #  define _PATH_MOUNT "/bin/mount"
  61 # endif
  62 # ifndef _PATH_UMOUNT
  63 #  define _PATH_UMOUNT "/bin/umount"
  64 # endif
  65
  66 #endif
  67
  68 const char *program;            /* Name of program */
  69 const char *device;             /* Device to install to */
  70 pid_t mypid;
  71 char *mntpath = NULL;           /* Path on which to mount */
  72 off_t filesystem_offset = 0;    /* Filesystem offset */
  73 #if DO_DIRECT_MOUNT
  74 int loop_fd = -1;               /* Loop device */
  75 #endif
  76
  77 void __attribute__((noreturn)) usage(void)
  78 {
  79   fprintf(stderr, "Usage: %s [-sf][-d directory][-o offset] device\n", program);
  80   exit(1);
  81 }
  82
  83 void __attribute__((noreturn)) die(const char *msg)
  84 {
  85   fprintf(stderr, "%s: %s\n", program, msg);
  86
  87 #if DO_DIRECT_MOUNT
  88   if ( loop_fd != -1 ) {
  89     ioctl(loop_fd, LOOP_CLR_FD, 0); /* Free loop device */
  90     close(loop_fd);
  91     loop_fd = -1;
  92   }
  93 #endif
  94
  95   if ( mntpath )
  96     unlink(mntpath);
  97
  98   exit(1);
  99 }
 100
 101 /*
 102  * read/write wrapper functions
 103  */
 104 ssize_t xpread(int fd, void *buf, size_t count, off_t offset)
 105 {
 106   char *bufp = (char *)buf;
 107   ssize_t rv;
 108   ssize_t done = 0;
 109
 110   while ( count ) {
 111     rv = pread(fd, bufp, count, offset);
 112     if ( rv == 0 ) {
 113       die("short read");
 114     } else if ( rv == -1 ) {
 115       if ( errno == EINTR ) {
 116         continue;
 117       } else {
 118         die(strerror(errno));
 119       }
 120     } else {
 121       bufp += rv;
 122       offset += rv;
 123       done += rv;
 124       count -= rv;
 125     }
 126   }
 127
 128   return done;
 129 }
 130
 131 ssize_t xpwrite(int fd, const void *buf, size_t count, off_t offset)
 132 {
 133   const char *bufp = (const char *)buf;
 134   ssize_t rv;
 135   ssize_t done = 0;
 136
 137   while ( count ) {
 138     rv = pwrite(fd, bufp, count, offset);
 139     if ( rv == 0 ) {
 140       die("short write");
 141     } else if ( rv == -1 ) {
 142       if ( errno == EINTR ) {
 143         continue;
 144       } else {
 145         die(strerror(errno));
 146       }
 147     } else {
 148       bufp += rv;
 149       offset += rv;
 150       done += rv;
 151       count -= rv;
 152     }
 153   }
 154
 155   return done;
 156 }
 157
 158 /*
 159  * Version of the read function suitable for libfat
 160  */
 161 int libfat_xpread(intptr_t pp, void *buf, size_t secsize, libfat_sector_t sector)
 162 {
 163   off_t offset = (off_t)sector * secsize + filesystem_offset;
 164   return xpread(pp, buf, secsize, offset);
 165 }
 166
 167 int main(int argc, char *argv[])
 168 {
 169   static unsigned char sectbuf[512];
 170   unsigned char *dp;
 171   const unsigned char *cdp;
 172   int dev_fd, fd;
 173   struct stat st;
 174   int nb, left;
 175   int err = 0;
 176   pid_t f, w;
 177   int status;
 178   char mntname[64], devfdname[64];
 179   char *ldlinux_name, **argp, *opt;
 180   int force = 0;                /* -f (force) option */
 181   const char *subdir = NULL;
 182   struct libfat_filesystem *fs;
 183   struct libfat_direntry dentry;
 184   libfat_sector_t s, *secp, sectors[65]; /* 65 is maximum possible */
 185   int32_t ldlinux_cluster;
 186   int nsectors = 0;
 187   const char *errmsg;
 188
 189   (void)argc;                   /* Unused */
 190
 191   program = argv[0];
 192   mypid = getpid();
 193
 194   device = NULL;
 195
 196   umask(077);
 197
 198   for ( argp = argv+1 ; *argp ; argp++ ) {
 199     if ( **argp == '-' ) {
 200       opt = *argp + 1;
 201       if ( !*opt )
 202         usage();
 203
 204       while ( *opt ) {
 205         if ( *opt == 's' ) {
 206           syslinux_make_stupid();       /* Use "safe, slow and stupid" code */
 207         } else if ( *opt == 'f' ) {
 208           force = 1;            /* Force install */
 209         } else if ( *opt == 'd' && argp[1] ) {
 210           subdir = *++argp;
 211         } else if ( *opt == 'o' && argp[1] ) {
 212           filesystem_offset = (off_t)strtoull(*++argp, NULL, 0); /* Byte offset */
 213         } else {
 214           usage();
 215         }
 216         opt++;
 217       }
 218     } else {
 219       if ( device )
 220         usage();
 221       device = *argp;
 222     }
 223   }
 224
 225   if ( !device )
 226     usage();
 227
 228   /*
 229    * First make sure we can open the device at all, and that we have
 230    * read/write permission.
 231    */
 232   dev_fd = open(device, O_RDWR);
 233   if ( dev_fd < 0 || fstat(dev_fd, &st) < 0 ) {
 234     perror(device);
 235     exit(1);
 236   }
 237
 238   if ( !force && !S_ISBLK(st.st_mode) && !S_ISREG(st.st_mode) ) {
 239     die("not a block device or regular file (use -f to override)");
 240   }
 241
 242   if ( !force && filesystem_offset && !S_ISREG(st.st_mode) ) {
 243     die("not a regular file and an offset specified (use -f to override)");
 244   }
 245
 246   xpread(dev_fd, sectbuf, 512, filesystem_offset);
 247   fsync(dev_fd);
 248
 249   /*
 250    * Check to see that what we got was indeed an MS-DOS boot sector/superblock
 251    */
 252   if( (errmsg = syslinux_check_bootsect(sectbuf)) ) {
 253     fprintf(stderr, "%s: %s\n", device, errmsg);
 254     exit(1);
 255   }
 256
 257   /*
 258    * Now mount the device.
 259    */
 260   if ( geteuid() ) {
 261     die("This program needs root privilege");
 262   } else {
 263     int i = 0;
 264     struct stat dst;
 265     int rv;
 266
 267     /* We're root or at least setuid.
 268        Make a temp dir and pass all the gunky options to mount. */
 269
 270     if ( chdir("/tmp") ) {
 271       perror(program);
 272       exit(1);
 273     }
 274
 275 #define TMP_MODE (S_IXUSR|S_IWUSR|S_IXGRP|S_IWGRP|S_IWOTH|S_IXOTH|S_ISVTX)
 276
 277     if ( stat(".", &dst) || !S_ISDIR(dst.st_mode) ||
 278          (dst.st_mode & TMP_MODE) != TMP_MODE ) {
 279       die("possibly unsafe /tmp permissions");
 280     }
 281
 282     for ( i = 0 ; ; i++ ) {
 283       snprintf(mntname, sizeof mntname, "syslinux.mnt.%lu.%d",
 284                (unsigned long)mypid, i);
 285
 286       if ( lstat(mntname, &dst) != -1 || errno != ENOENT )
 287         continue;
 288
 289       rv = mkdir(mntname, 0000);
 290
 291       if ( rv == -1 ) {
 292         if ( errno == EEXIST || errno == EINTR )
 293           continue;
 294         perror(program);
 295         exit(1);
 296       }
 297
 298       if ( lstat(mntname, &dst) || dst.st_mode != (S_IFDIR|0000) ||
 299            dst.st_uid != 0 ) {
 300         die("someone is trying to symlink race us!");
 301       }
 302       break;                    /* OK, got something... */
 303     }
 304
 305     mntpath = mntname;
 306
 307 #if DO_DIRECT_MOUNT
 308     if ( S_ISREG(st.st_mode) ) {
 309       /* It's file, need to mount it loopback */
 310       unsigned int n = 0;
 311       struct loop_info64 loopinfo;
 312
 313       for ( n = 0 ; loop_fd < 0 ; n++ ) {
 314         snprintf(devfdname, sizeof devfdname, "/dev/loop%u", n);
 315         loop_fd = open(devfdname, O_RDWR);
 316         if ( loop_fd < 0 && errno == ENOENT ) {
 317           die("no available loopback device!");
 318         }
 319         if ( ioctl(loop_fd, LOOP_SET_FD, (void *)dev_fd) ) {
 320           close(loop_fd); loop_fd = -1;
 321           if ( errno != EBUSY )
 322             die("cannot set up loopback device");
 323           else
 324             continue;
 325         }
 326
 327         if ( ioctl(loop_fd, LOOP_GET_STATUS64, &loopinfo) ||
 328              (loopinfo.lo_offset = filesystem_offset,
 329               ioctl(loop_fd, LOOP_SET_STATUS64, &loopinfo)) )
 330           die("cannot set up loopback device");
 331       }
 332     } else {
 333       snprintf(devfdname, sizeof devfdname, "/proc/%lu/fd/%d",
 334                (unsigned long)mypid, dev_fd);
 335     }
 336
 337     if ( mount(devfdname, mntpath, "msdos",
 338                MS_NOEXEC|MS_NOSUID, "umask=077,quiet") )
 339       die("could not mount filesystem");
 340
 341 #else
 342
 343     snprintf(devfdname, sizeof devfdname, "/proc/%lu/fd/%d",
 344              (unsigned long)mypid, dev_fd);
 345
 346     f = fork();
 347     if ( f < 0 ) {
 348       perror(program);
 349       rmdir(mntpath);
 350       exit(1);
 351     } else if ( f == 0 ) {
 352       char mnt_opts[128];
 353       if ( S_ISREG(st.st_mode) ) {
 354         snprintf(mnt_opts, sizeof mnt_opts, "rw,nodev,noexec,loop,offset=%llu,umask=077,quiet",
 355                  (unsigned long long)filesystem_offset);
 356       } else {
 357         snprintf(mnt_opts, sizeof mnt_opts, "rw,nodev,noexec,umask=077,quiet");
 358       }
 359       execl(_PATH_MOUNT, _PATH_MOUNT, "-t", "msdos", "-o", mnt_opts,\
 360             devfdname, mntpath, NULL);
 361       _exit(255);               /* execl failed */
 362     }
 363
 364     w = waitpid(f, &status, 0);
 365     if ( w != f || status ) {
 366       rmdir(mntpath);
 367       exit(1);                  /* Mount failed */
 368     }
 369
 370 #endif
 371   }
 372
 373   ldlinux_name = alloca(strlen(mntpath)+14);
 374   if ( !ldlinux_name ) {
 375     perror(program);
 376     err = 1;
 377     goto umount;
 378   }
 379   sprintf(ldlinux_name, "%s//ldlinux.sys", mntpath);
 380
 381   unlink(ldlinux_name);
 382   fd = open(ldlinux_name, O_WRONLY|O_CREAT|O_TRUNC, 0444);
 383   if ( fd < 0 ) {
 384     perror(device);
 385     err = 1;
 386     goto umount;
 387   }
 388
 389   cdp = syslinux_ldlinux;
 390   left = syslinux_ldlinux_len;
 391   while ( left ) {
 392     nb = write(fd, cdp, left);
 393     if ( nb == -1 && errno == EINTR )
 394       continue;
 395     else if ( nb <= 0 ) {
 396       perror(device);
 397       err = 1;
 398       goto umount;
 399     }
 400
 401     dp += nb;
 402     left -= nb;
 403   }
 404
 405   /*
 406    * I don't understand why I need this.  Does the DOS filesystems
 407    * not honour the mode passed to open()?
 408    */
 409   fchmod(fd, 0400);
 410
 411   close(fd);
 412
 413   sync();
 414
 415   /*
 416    * Now, use libfat to create a block map.  This probably
 417    * should be changed to use ioctl(...,FIBMAP,...) since
 418    * this is supposed to be a simple, privileged version
 419    * of the installer.
 420    */
 421   fs = libfat_open(libfat_xpread, dev_fd);
 422   ldlinux_cluster = libfat_searchdir(fs, 0, "LDLINUX SYS", &dentry);
 423   secp = sectors;
 424   nsectors = 0;
 425   s = libfat_clustertosector(fs, ldlinux_cluster);
 426   while ( s && nsectors < 65 ) {
 427     *secp++ = s;
 428     nsectors++;
 429     s = libfat_nextsector(fs, s);
 430   }
 431   libfat_close(fs);
 432
 433   /* Move ldlinux.sys to the desired location */
 434   if (subdir) {
 435     char *new_ldlinux_name = alloca(strlen(mntpath)+
 436                                     strlen(subdir)+15);
 437     int mov_err = 1;
 438
 439     if ( new_ldlinux_name ) {
 440       sprintf(new_ldlinux_name, "%s//%s//ldlinux.sys", mntpath, subdir);
 441
 442       if (!rename(ldlinux_name, new_ldlinux_name))
 443         mov_err = 0;
 444     }
 445
 446     if (mov_err)
 447       fprintf(stderr, "%s: warning: unable to move ldlinux.sys: %s\n",
 448               device, strerror(errno));
 449   }
 450
 451 umount:
 452 #if DO_DIRECT_MOUNT
 453
 454   if ( umount2(mntpath, 0) )
 455     die("could not umount path");
 456
 457   if ( loop_fd != -1 ) {
 458     ioctl(loop_fd, LOOP_CLR_FD, 0); /* Free loop device */
 459     close(loop_fd);
 460     loop_fd = -1;
 461   }
 462
 463 #else
 464
 465   f = fork();
 466   if ( f < 0 ) {
 467     perror("fork");
 468     exit(1);
 469   } else if ( f == 0 ) {
 470     execl(_PATH_UMOUNT, _PATH_UMOUNT, mntpath, NULL);
 471   }
 472
 473   w = waitpid(f, &status, 0);
 474   if ( w != f || status ) {
 475     exit(1);
 476   }
 477
 478 #endif
 479
 480   sync();
 481   rmdir(mntpath);
 482
 483   if ( err )
 484     exit(err);
 485
 486   /*
 487    * Patch ldlinux.sys and the boot sector
 488    */
 489   syslinux_patch(sectors, nsectors);
 490
 491   /*
 492    * Write the now-patched first sector of ldlinux.sys
 493    */
 494   xpwrite(dev_fd, syslinux_ldlinux, 512, filesystem_offset + ((off_t)sectors[0] << 9));
 495
 496   /*
 497    * Patch the root directory to set attributes to
 498    * HIDDEN|SYSTEM|READONLY
 499    */
 500   {
 501     const unsigned char attrib = 0x07;
 502     xpwrite(dev_fd, &attrib, 1, ((off_t)dentry.sector << 9)+dentry.offset+11);
 503   }
 504
 505   /*
 506    * To finish up, write the boot sector
 507    */
 508
 509   /* Read the superblock again since it might have changed while mounted */
 510   xpread(dev_fd, sectbuf, 512, filesystem_offset);
 511
 512   /* Copy the syslinux code into the boot sector */
 513   syslinux_make_bootsect(sectbuf);
 514
 515   /* Write new boot sector */
 516   xpwrite(dev_fd, sectbuf, 512, filesystem_offset);
 517
 518   close(dev_fd);
 519   sync();
 520
 521   /* Done! */
 522
 523   return 0;
 524 }