fs/namei.c

/* */
This source file includes following definitions.
getname
putname
permission
lookup
follow_link
dir_namei
_namei
lnamei
namei
open_namei
do_mknod
sys_mknod
do_mkdir
sys_mkdir
do_rmdir
sys_rmdir
do_unlink
sys_unlink
do_symlink
sys_symlink
do_link
sys_link
do_rename
sys_rename
   1 /*
   2  *  linux/fs/namei.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6 
   7 /*
   8  * Some corrections by tytso.
   9  */
  10 
  11 #include <asm/segment.h>
  12 
  13 #include <linux/errno.h>
  14 #include <linux/sched.h>
  15 #include <linux/kernel.h>
  16 #include <linux/string.h>
  17 #include <linux/fcntl.h>
  18 #include <linux/stat.h>
  19 
  20 #define ACC_MODE(x) ("\000\004\002\006"[(x)&O_ACCMODE])
  21 
  22 /*
  23  * In order to reduce some races, while at the same time doing additional
  24  * checking and hopefully speeding things up, we copy filenames to the
  25  * kernel data space before using them..
  26  *
  27  * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
  28  */
  29 int getname(const char * filename, char **result)
     /*  */
  30 {
  31         int error;
  32         unsigned long i, page;
  33         char * tmp, c;
  34 
  35         i = (unsigned long) filename;
  36         if (!i || i >= TASK_SIZE)
  37                 return -EFAULT;
  38         i = TASK_SIZE - i;
  39         error = -EFAULT;
  40         if (i > PAGE_SIZE) {
  41                 i = PAGE_SIZE;
  42                 error = -ENAMETOOLONG;
  43         }
  44         c = get_fs_byte(filename++);
  45         if (!c)
  46                 return -ENOENT;
  47         page = __get_free_page(GFP_KERNEL);
  48         if (!page)
  49                 return -ENOMEM;
  50         *result = tmp = (char *) page;
  51         while (--i) {
  52                 *(tmp++) = c;
  53                 c = get_fs_byte(filename++);
  54                 if (!c) {
  55                         *tmp = '\0';
  56                         return 0;
  57                 }
  58         }
  59         free_page(page);
  60         return error;
  61 }
  62 
  63 void putname(char * name)
     /*  */
  64 {
  65         free_page((unsigned long) name);
  66 }
  67 
  68 /*
  69  *      permission()
  70  *
  71  * is used to check for read/write/execute permissions on a file.
  72  * I don't know if we should look at just the euid or both euid and
  73  * uid, but that should be easily changed.
  74  */
  75 int permission(struct inode * inode,int mask)
     /*  */
  76 {
  77         int mode = inode->i_mode;
  78 
  79 /* special case: not even root can read/write a deleted file */
  80         if (inode->i_dev && !inode->i_nlink)
  81                 return 0;
  82         else if (inode->i_op && inode->i_op->permission)
  83                 return inode->i_op->permission(inode, mask);
  84         else if (current->euid == inode->i_uid)
  85                 mode >>= 6;
  86         else if (in_group_p(inode->i_gid))
  87                 mode >>= 3;
  88         if (((mode & mask & 0007) == mask) || suser())
  89                 return 1;
  90         return 0;
  91 }
  92 
  93 /*
  94  * lookup() looks up one part of a pathname, using the fs-dependent
  95  * routines (currently minix_lookup) for it. It also checks for
  96  * fathers (pseudo-roots, mount-points)
  97  */
  98 int lookup(struct inode * dir,const char * name, int len,
     /*  */
  99         struct inode ** result)
 100 {
 101         struct super_block * sb;
 102         int perm;
 103 
 104         *result = NULL;
 105         if (!dir)
 106                 return -ENOENT;
 107 /* check permissions before traversing mount-points */
 108         perm = permission(dir,MAY_EXEC);
 109         if (len==2 && name[0] == '.' && name[1] == '.') {
 110                 if (dir == current->root) {
 111                         *result = dir;
 112                         return 0;
 113                 } else if ((sb = dir->i_sb) && (dir == sb->s_mounted)) {
 114                         sb = dir->i_sb;
 115                         iput(dir);
 116                         dir = sb->s_covered;
 117                         if (!dir)
 118                                 return -ENOENT;
 119                         dir->i_count++;
 120                 }
 121         }
 122         if (!dir->i_op || !dir->i_op->lookup) {
 123                 iput(dir);
 124                 return -ENOTDIR;
 125         }
 126         if (!perm) {
 127                 iput(dir);
 128                 return -EACCES;
 129         }
 130         if (!len) {
 131                 *result = dir;
 132                 return 0;
 133         }
 134         return dir->i_op->lookup(dir,name,len,result);
 135 }
 136 
 137 int follow_link(struct inode * dir, struct inode * inode,
     /*  */
 138         int flag, int mode, struct inode ** res_inode)
 139 {
 140         if (!dir || !inode) {
 141                 iput(dir);
 142                 iput(inode);
 143                 *res_inode = NULL;
 144                 return -ENOENT;
 145         }
 146         if (!inode->i_op || !inode->i_op->follow_link) {
 147                 iput(dir);
 148                 *res_inode = inode;
 149                 return 0;
 150         }
 151         return inode->i_op->follow_link(dir,inode,flag,mode,res_inode);
 152 }
 153 
 154 /*
 155  *      dir_namei()
 156  *
 157  * dir_namei() returns the inode of the directory of the
 158  * specified name, and the name within that directory.
 159  */
 160 static int dir_namei(const char * pathname, int * namelen, const char ** name,
     /*  */
 161         struct inode * base, struct inode ** res_inode)
 162 {
 163         char c;
 164         const char * thisname;
 165         int len,error;
 166         struct inode * inode;
 167 
 168         *res_inode = NULL;
 169         if (!base) {
 170                 base = current->pwd;
 171                 base->i_count++;
 172         }
 173         if ((c = *pathname) == '/') {
 174                 iput(base);
 175                 base = current->root;
 176                 pathname++;
 177                 base->i_count++;
 178         }
 179         while (1) {
 180                 thisname = pathname;
 181                 for(len=0;(c = *(pathname++))&&(c != '/');len++)
 182                         /* nothing */ ;
 183                 if (!c)
 184                         break;
 185                 base->i_count++;
 186                 error = lookup(base,thisname,len,&inode);
 187                 if (error) {
 188                         iput(base);
 189                         return error;
 190                 }
 191                 error = follow_link(base,inode,0,0,&base);
 192                 if (error)
 193                         return error;
 194         }
 195         if (!base->i_op || !base->i_op->lookup) {
 196                 iput(base);
 197                 return -ENOTDIR;
 198         }
 199         *name = thisname;
 200         *namelen = len;
 201         *res_inode = base;
 202         return 0;
 203 }
 204 
 205 static int _namei(const char * pathname, struct inode * base,
     /*  */
 206         int follow_links, struct inode ** res_inode)
 207 {
 208         const char * basename;
 209         int namelen,error;
 210         struct inode * inode;
 211 
 212         *res_inode = NULL;
 213         error = dir_namei(pathname,&namelen,&basename,base,&base);
 214         if (error)
 215                 return error;
 216         base->i_count++;        /* lookup uses up base */
 217         error = lookup(base,basename,namelen,&inode);
 218         if (error) {
 219                 iput(base);
 220                 return error;
 221         }
 222         if (follow_links) {
 223                 error = follow_link(base,inode,0,0,&inode);
 224                 if (error)
 225                         return error;
 226         } else
 227                 iput(base);
 228         *res_inode = inode;
 229         return 0;
 230 }
 231 
 232 int lnamei(const char * pathname, struct inode ** res_inode)
     /*  */
 233 {
 234         int error;
 235         char * tmp;
 236 
 237         error = getname(pathname,&tmp);
 238         if (!error) {
 239                 error = _namei(tmp,NULL,0,res_inode);
 240                 putname(tmp);
 241         }
 242         return error;
 243 }
 244 
 245 /*
 246  *      namei()
 247  *
 248  * is used by most simple commands to get the inode of a specified name.
 249  * Open, link etc use their own routines, but this is enough for things
 250  * like 'chmod' etc.
 251  */
 252 int namei(const char * pathname, struct inode ** res_inode)
     /*  */
 253 {
 254         int error;
 255         char * tmp;
 256 
 257         error = getname(pathname,&tmp);
 258         if (!error) {
 259                 error = _namei(tmp,NULL,1,res_inode);
 260                 putname(tmp);
 261         }
 262         return error;
 263 }
 264 
 265 /*
 266  *      open_namei()
 267  *
 268  * namei for open - this is in fact almost the whole open-routine.
 269  *
 270  * Note that the low bits of "flag" aren't the same asin the open
 271  * system call - they are 00 - no permissions needed
 272  *                        01 - read permission needed
 273  *                        10 - write permission needed
 274  *                        11 - read/write permissions needed
 275  * which is a lot more logical, and also allows the "no perm" needed
 276  * for symlinks (where the permissions are checked later).
 277  */
 278 int open_namei(const char * pathname, int flag, int mode,
     /*  */
 279         struct inode ** res_inode, struct inode * base)
 280 {
 281         const char * basename;
 282         int namelen,error,i;
 283         struct inode * dir, *inode;
 284         struct task_struct ** p;
 285 
 286         mode &= 07777 & ~current->umask;
 287         mode |= S_IFREG;
 288         error = dir_namei(pathname,&namelen,&basename,base,&dir);
 289         if (error)
 290                 return error;
 291         if (!namelen) {                 /* special case: '/usr/' etc */
 292                 if (flag & 2) {
 293                         iput(dir);
 294                         return -EISDIR;
 295                 }
 296                 /* thanks to Paul Pluzhnikov for noticing this was missing.. */
 297                 if (!permission(dir,ACC_MODE(flag))) {
 298                         iput(dir);
 299                         return -EACCES;
 300                 }
 301                 *res_inode=dir;
 302                 return 0;
 303         }
 304         for (i = 0; i < 5; i++) {       /* races... */
 305                 dir->i_count++;         /* lookup eats the dir */
 306                 error = lookup(dir,basename,namelen,&inode);
 307                 if (!error)
 308                         break;
 309                 if (!(flag & O_CREAT)) {
 310                         iput(dir);
 311                         return error;
 312                 }
 313                 if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 314                         iput(dir);
 315                         return -EACCES;
 316                 }
 317                 if (!dir->i_op || !dir->i_op->create) {
 318                         iput(dir);
 319                         return -EACCES;
 320                 }
 321                 if (IS_RDONLY(dir)) {
 322                         iput(dir);
 323                         return -EROFS;
 324                 }
 325                 dir->i_count++;         /* create eats the dir */
 326                 error = dir->i_op->create(dir,basename,namelen,mode,res_inode);
 327                 if (error != -EEXIST) {
 328                         iput(dir);
 329                         return error;
 330                 }
 331         }
 332         if (error) {
 333                 iput(dir);
 334                 return error;
 335         }
 336         if ((flag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL)) {
 337                 iput(dir);
 338                 iput(inode);
 339                 return -EEXIST;
 340         }
 341         error = follow_link(dir,inode,flag,mode,&inode);
 342         if (error)
 343                 return error;
 344         if (S_ISDIR(inode->i_mode) && (flag & 2)) {
 345                 iput(inode);
 346                 return -EISDIR;
 347         }
 348         if (!permission(inode,ACC_MODE(flag))) {
 349                 iput(inode);
 350                 return -EACCES;
 351         }
 352         if (S_ISBLK(inode->i_mode) || S_ISCHR(inode->i_mode)) {
 353                 if (IS_NODEV(inode)) {
 354                         iput(inode);
 355                         return -EACCES;
 356                 }
 357         } else {
 358                 if (IS_RDONLY(inode) && (flag & 2)) {
 359                         iput(inode);
 360                         return -EROFS;
 361                 }
 362         }
 363         if ((inode->i_count > 1) && (flag & 2)) {
 364                 for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
 365                         struct vm_area_struct * mpnt;
 366                         if (!*p)
 367                                 continue;
 368                         if (inode == (*p)->executable) {
 369                                 iput(inode);
 370                                 return -ETXTBSY;
 371                         }
 372                         for(mpnt = (*p)->mmap; mpnt; mpnt = mpnt->vm_next) {
 373                                 if (inode == mpnt->vm_inode) {
 374                                         iput(inode);
 375                                         return -ETXTBSY;
 376                                 }
 377                         }
 378                 }
 379         }
 380         *res_inode = inode;
 381         return 0;
 382 }
 383 
 384 int do_mknod(const char * filename, int mode, dev_t dev)
     /*  */
 385 {
 386         const char * basename;
 387         int namelen, error;
 388         struct inode * dir;
 389 
 390         mode &= ~current->umask;
 391         error = dir_namei(filename,&namelen,&basename, NULL, &dir);
 392         if (error)
 393                 return error;
 394         if (!namelen) {
 395                 iput(dir);
 396                 return -ENOENT;
 397         }
 398         if (IS_RDONLY(dir)) {
 399                 iput(dir);
 400                 return -EROFS;
 401         }
 402         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 403                 iput(dir);
 404                 return -EACCES;
 405         }
 406         if (!dir->i_op || !dir->i_op->mknod) {
 407                 iput(dir);
 408                 return -EPERM;
 409         }
 410         return dir->i_op->mknod(dir,basename,namelen,mode,dev);
 411 }
 412 
 413 extern "C" int sys_mknod(const char * filename, int mode, dev_t dev)
     /*  */
 414 {
 415         int error;
 416         char * tmp;
 417 
 418         if (S_ISDIR(mode)  || (!S_ISFIFO(mode) && !suser()))
 419                 return -EPERM;
 420         error = getname(filename,&tmp);
 421         if (!error) {
 422                 error = do_mknod(tmp,mode,dev);
 423                 putname(tmp);
 424         }
 425         return error;
 426 }
 427 
 428 static int do_mkdir(const char * pathname, int mode)
     /*  */
 429 {
 430         const char * basename;
 431         int namelen, error;
 432         struct inode * dir;
 433 
 434         error = dir_namei(pathname,&namelen,&basename,NULL,&dir);
 435         if (error)
 436                 return error;
 437         if (!namelen) {
 438                 iput(dir);
 439                 return -ENOENT;
 440         }
 441         if (IS_RDONLY(dir)) {
 442                 iput(dir);
 443                 return -EROFS;
 444         }
 445         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 446                 iput(dir);
 447                 return -EACCES;
 448         }
 449         if (!dir->i_op || !dir->i_op->mkdir) {
 450                 iput(dir);
 451                 return -EPERM;
 452         }
 453         return dir->i_op->mkdir(dir,basename,namelen,mode);
 454 }
 455 
 456 extern "C" int sys_mkdir(const char * pathname, int mode)
     /*  */
 457 {
 458         int error;
 459         char * tmp;
 460 
 461         error = getname(pathname,&tmp);
 462         if (!error) {
 463                 error = do_mkdir(tmp,mode);
 464                 putname(tmp);
 465         }
 466         return error;
 467 }
 468 
 469 static int do_rmdir(const char * name)
     /*  */
 470 {
 471         const char * basename;
 472         int namelen, error;
 473         struct inode * dir;
 474 
 475         error = dir_namei(name,&namelen,&basename,NULL,&dir);
 476         if (error)
 477                 return error;
 478         if (!namelen) {
 479                 iput(dir);
 480                 return -ENOENT;
 481         }
 482         if (IS_RDONLY(dir)) {
 483                 iput(dir);
 484                 return -EROFS;
 485         }
 486         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 487                 iput(dir);
 488                 return -EACCES;
 489         }
 490         if (!dir->i_op || !dir->i_op->rmdir) {
 491                 iput(dir);
 492                 return -EPERM;
 493         }
 494         return dir->i_op->rmdir(dir,basename,namelen);
 495 }
 496 
 497 extern "C" int sys_rmdir(const char * pathname)
     /*  */
 498 {
 499         int error;
 500         char * tmp;
 501 
 502         error = getname(pathname,&tmp);
 503         if (!error) {
 504                 error = do_rmdir(tmp);
 505                 putname(tmp);
 506         }
 507         return error;
 508 }
 509 
 510 static int do_unlink(const char * name)
     /*  */
 511 {
 512         const char * basename;
 513         int namelen, error;
 514         struct inode * dir;
 515 
 516         error = dir_namei(name,&namelen,&basename,NULL,&dir);
 517         if (error)
 518                 return error;
 519         if (!namelen) {
 520                 iput(dir);
 521                 return -EPERM;
 522         }
 523         if (IS_RDONLY(dir)) {
 524                 iput(dir);
 525                 return -EROFS;
 526         }
 527         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 528                 iput(dir);
 529                 return -EACCES;
 530         }
 531         if (!dir->i_op || !dir->i_op->unlink) {
 532                 iput(dir);
 533                 return -EPERM;
 534         }
 535         return dir->i_op->unlink(dir,basename,namelen);
 536 }
 537 
 538 extern "C" int sys_unlink(const char * pathname)
     /*  */
 539 {
 540         int error;
 541         char * tmp;
 542 
 543         error = getname(pathname,&tmp);
 544         if (!error) {
 545                 error = do_unlink(tmp);
 546                 putname(tmp);
 547         }
 548         return error;
 549 }
 550 
 551 static int do_symlink(const char * oldname, const char * newname)
     /*  */
 552 {
 553         struct inode * dir;
 554         const char * basename;
 555         int namelen, error;
 556 
 557         error = dir_namei(newname,&namelen,&basename,NULL,&dir);
 558         if (error)
 559                 return error;
 560         if (!namelen) {
 561                 iput(dir);
 562                 return -ENOENT;
 563         }
 564         if (IS_RDONLY(dir)) {
 565                 iput(dir);
 566                 return -EROFS;
 567         }
 568         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 569                 iput(dir);
 570                 return -EACCES;
 571         }
 572         if (!dir->i_op || !dir->i_op->symlink) {
 573                 iput(dir);
 574                 return -EPERM;
 575         }
 576         return dir->i_op->symlink(dir,basename,namelen,oldname);
 577 }
 578 
 579 extern "C" int sys_symlink(const char * oldname, const char * newname)
     /*  */
 580 {
 581         int error;
 582         char * from, * to;
 583 
 584         error = getname(oldname,&from);
 585         if (!error) {
 586                 error = getname(newname,&to);
 587                 if (!error) {
 588                         error = do_symlink(from,to);
 589                         putname(to);
 590                 }
 591                 putname(from);
 592         }
 593         return error;
 594 }
 595 
 596 static int do_link(struct inode * oldinode, const char * newname)
     /*  */
 597 {
 598         struct inode * dir;
 599         const char * basename;
 600         int namelen, error;
 601 
 602         error = dir_namei(newname,&namelen,&basename,NULL,&dir);
 603         if (error) {
 604                 iput(oldinode);
 605                 return error;
 606         }
 607         if (!namelen) {
 608                 iput(oldinode);
 609                 iput(dir);
 610                 return -EPERM;
 611         }
 612         if (IS_RDONLY(dir)) {
 613                 iput(oldinode);
 614                 iput(dir);
 615                 return -EROFS;
 616         }
 617         if (dir->i_dev != oldinode->i_dev) {
 618                 iput(dir);
 619                 iput(oldinode);
 620                 return -EXDEV;
 621         }
 622         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 623                 iput(dir);
 624                 iput(oldinode);
 625                 return -EACCES;
 626         }
 627         if (!dir->i_op || !dir->i_op->link) {
 628                 iput(dir);
 629                 iput(oldinode);
 630                 return -EPERM;
 631         }
 632         return dir->i_op->link(oldinode, dir, basename, namelen);
 633 }
 634 
 635 extern "C" int sys_link(const char * oldname, const char * newname)
     /*  */
 636 {
 637         int error;
 638         char * to;
 639         struct inode * oldinode;
 640 
 641         error = namei(oldname, &oldinode);
 642         if (error)
 643                 return error;
 644         error = getname(newname,&to);
 645         if (!error) {
 646                 error = do_link(oldinode,to);
 647                 putname(to);
 648         }
 649         return error;
 650 }
 651 
 652 static int do_rename(const char * oldname, const char * newname)
     /*  */
 653 {
 654         struct inode * old_dir, * new_dir;
 655         const char * old_base, * new_base;
 656         int old_len, new_len, error;
 657 
 658         error = dir_namei(oldname,&old_len,&old_base,NULL,&old_dir);
 659         if (error)
 660                 return error;
 661         if (!permission(old_dir,MAY_WRITE | MAY_EXEC)) {
 662                 iput(old_dir);
 663                 return -EACCES;
 664         }
 665         if (!old_len || (old_base[0] == '.' &&
 666             (old_len == 1 || (old_base[1] == '.' &&
 667              old_len == 2)))) {
 668                 iput(old_dir);
 669                 return -EPERM;
 670         }
 671         error = dir_namei(newname,&new_len,&new_base,NULL,&new_dir);
 672         if (error) {
 673                 iput(old_dir);
 674                 return error;
 675         }
 676         if (!permission(new_dir,MAY_WRITE | MAY_EXEC)) {
 677                 iput(old_dir);
 678                 iput(new_dir);
 679                 return -EACCES;
 680         }
 681         if (!new_len || (new_base[0] == '.' &&
 682             (new_len == 1 || (new_base[1] == '.' &&
 683              new_len == 2)))) {
 684                 iput(old_dir);
 685                 iput(new_dir);
 686                 return -EPERM;
 687         }
 688         if (new_dir->i_dev != old_dir->i_dev) {
 689                 iput(old_dir);
 690                 iput(new_dir);
 691                 return -EXDEV;
 692         }
 693         if (IS_RDONLY(new_dir) || IS_RDONLY(old_dir)) {
 694                 iput(old_dir);
 695                 iput(new_dir);
 696                 return -EROFS;
 697         }
 698         if (!old_dir->i_op || !old_dir->i_op->rename) {
 699                 iput(old_dir);
 700                 iput(new_dir);
 701                 return -EPERM;
 702         }
 703         return old_dir->i_op->rename(old_dir, old_base, old_len, 
 704                 new_dir, new_base, new_len);
 705 }
 706 
 707 extern "C" int sys_rename(const char * oldname, const char * newname)
     /*  */
 708 {
 709         int error;
 710         char * from, * to;
 711 
 712         error = getname(oldname,&from);
 713         if (!error) {
 714                 error = getname(newname,&to);
 715                 if (!error) {
 716                         error = do_rename(from,to);
 717                         putname(to);
 718                 }
 719                 putname(from);
 720         }
 721         return error;
 722 }
/* */
root/fs/namei.c

DEFINITIONS
