fs/namei.c

/* */
This source file includes following definitions.
permission
lookup
follow_link
dir_namei
_namei
lnamei
namei
open_namei
do_mknod
sys_mknod
sys_mkdir
sys_rmdir
sys_unlink
sys_symlink
sys_link
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  * comment out this line if you want names > MINIX_NAME_LEN chars to be
  24  * truncated. Else they will be disallowed.
  25  */
  26 /* #define NO_TRUNCATE */
  27 
  28 /*
  29  *      permission()
  30  *
  31  * is used to check for read/write/execute permissions on a file.
  32  * I don't know if we should look at just the euid or both euid and
  33  * uid, but that should be easily changed.
  34  */
  35 int permission(struct inode * inode,int mask)
     /*  */
  36 {
  37         int mode = inode->i_mode;
  38 
  39 /* special case: not even root can read/write a deleted file */
  40         if (inode->i_dev && !inode->i_nlink)
  41                 return 0;
  42         else if (current->euid == inode->i_uid)
  43                 mode >>= 6;
  44         else if (in_group_p(inode->i_gid))
  45                 mode >>= 3;
  46         if (((mode & mask & 0007) == mask) || suser())
  47                 return 1;
  48         return 0;
  49 }
  50 
  51 /*
  52  * lookup() looks up one part of a pathname, using the fs-dependent
  53  * routines (currently minix_lookup) for it. It also checks for
  54  * fathers (pseudo-roots, mount-points)
  55  */
  56 int lookup(struct inode * dir,const char * name, int len,
     /*  */
  57         struct inode ** result)
  58 {
  59         struct super_block * sb;
  60 
  61         *result = NULL;
  62         if (len==2 && get_fs_byte(name)=='.' && get_fs_byte(name+1)=='.') {
  63                 if (dir == current->root)
  64                         len = 1;
  65                 else if ((sb = dir->i_sb) && (dir == sb->s_mounted)) {
  66                         sb = dir->i_sb;
  67                         iput(dir);
  68                         if (dir = sb->s_covered)
  69                                 dir->i_count++;
  70                 }
  71         }
  72         if (!dir)
  73                 return -ENOENT;
  74         if (!dir->i_op || !dir->i_op->lookup) {
  75                 iput(dir);
  76                 return -ENOTDIR;
  77         }
  78         if (!permission(dir,MAY_EXEC)) {
  79                 iput(dir);
  80                 return -EACCES;
  81         }
  82         if (!len) {
  83                 *result = dir;
  84                 return 0;
  85         }
  86         return dir->i_op->lookup(dir,name,len,result);
  87 }
  88 
  89 int follow_link(struct inode * dir, struct inode * inode,
     /*  */
  90         int flag, int mode, struct inode ** res_inode)
  91 {
  92         if (!dir || !inode) {
  93                 iput(dir);
  94                 iput(inode);
  95                 *res_inode = NULL;
  96                 return -ENOENT;
  97         }
  98         if (!inode->i_op || !inode->i_op->follow_link) {
  99                 iput(dir);
 100                 *res_inode = inode;
 101                 return 0;
 102         }
 103         return inode->i_op->follow_link(dir,inode,flag,mode,res_inode);
 104 }
 105 
 106 /*
 107  *      dir_namei()
 108  *
 109  * dir_namei() returns the inode of the directory of the
 110  * specified name, and the name within that directory.
 111  */
 112 static int dir_namei(const char * pathname, int * namelen, const char ** name,
     /*  */
 113         struct inode * base, struct inode ** res_inode)
 114 {
 115         char c;
 116         const char * thisname;
 117         int len,error;
 118         struct inode * inode;
 119 
 120         *res_inode = NULL;
 121         if (!base) {
 122                 base = current->pwd;
 123                 base->i_count++;
 124         }
 125         if ((c=get_fs_byte(pathname))=='/') {
 126                 iput(base);
 127                 base = current->root;
 128                 pathname++;
 129                 base->i_count++;
 130         }
 131         while (1) {
 132                 thisname = pathname;
 133                 for(len=0;(c=get_fs_byte(pathname++))&&(c!='/');len++)
 134                         /* nothing */ ;
 135                 if (!c)
 136                         break;
 137                 base->i_count++;
 138                 error = lookup(base,thisname,len,&inode);
 139                 if (error) {
 140                         iput(base);
 141                         return error;
 142                 }
 143                 error = follow_link(base,inode,0,0,&base);
 144                 if (error)
 145                         return error;
 146         }
 147         *name = thisname;
 148         *namelen = len;
 149         *res_inode = base;
 150         return 0;
 151 }
 152 
 153 static int _namei(const char * pathname, struct inode * base,
     /*  */
 154         int follow_links, struct inode ** res_inode)
 155 {
 156         const char * basename;
 157         int namelen,error;
 158         struct inode * inode;
 159 
 160         *res_inode = NULL;
 161         error = dir_namei(pathname,&namelen,&basename,base,&base);
 162         if (error)
 163                 return error;
 164         base->i_count++;        /* lookup uses up base */
 165         error = lookup(base,basename,namelen,&inode);
 166         if (error) {
 167                 iput(base);
 168                 return error;
 169         }
 170         if (follow_links) {
 171                 error = follow_link(base,inode,0,0,&inode);
 172                 if (error)
 173                         return error;
 174         } else
 175                 iput(base);
 176         *res_inode = inode;
 177         return 0;
 178 }
 179 
 180 int lnamei(const char * pathname, struct inode ** res_inode)
     /*  */
 181 {
 182         return _namei(pathname,NULL,0,res_inode);
 183 }
 184 
 185 /*
 186  *      namei()
 187  *
 188  * is used by most simple commands to get the inode of a specified name.
 189  * Open, link etc use their own routines, but this is enough for things
 190  * like 'chmod' etc.
 191  */
 192 int namei(const char * pathname, struct inode ** res_inode)
     /*  */
 193 {
 194         return _namei(pathname,NULL,1,res_inode);
 195 }
 196 
 197 /*
 198  *      open_namei()
 199  *
 200  * namei for open - this is in fact almost the whole open-routine.
 201  *
 202  * Note that the low bits of "flag" aren't the same asin the open
 203  * system call - they are 00 - no permissions needed
 204  *                        01 - read permission needed
 205  *                        10 - write permission needed
 206  *                        11 - read/write permissions needed
 207  * which is a lot more logical, and also allows the "no perm" needed
 208  * for symlinks (where the permissions are checked later).
 209  */
 210 int open_namei(const char * pathname, int flag, int mode,
     /*  */
 211         struct inode ** res_inode, struct inode * base)
 212 {
 213         const char * basename;
 214         int namelen,error,i;
 215         struct inode * dir, *inode;
 216         struct task_struct ** p;
 217 
 218         mode &= 07777 & ~current->umask;
 219         mode |= S_IFREG;
 220         error = dir_namei(pathname,&namelen,&basename,base,&dir);
 221         if (error)
 222                 return error;
 223         if (!namelen) {                 /* special case: '/usr/' etc */
 224                 if (!(flag & 2)) {
 225                         *res_inode=dir;
 226                         return 0;
 227                 }
 228                 iput(dir);
 229                 return -EISDIR;
 230         }
 231         dir->i_count++;         /* lookup eats the dir */
 232         error = lookup(dir,basename,namelen,&inode);
 233         if (error) {
 234                 if (!(flag & O_CREAT)) {
 235                         iput(dir);
 236                         return error;
 237                 }
 238                 if (!permission(dir,MAY_WRITE)) {
 239                         iput(dir);
 240                         return -EACCES;
 241                 }
 242                 if (!dir->i_op || !dir->i_op->create) {
 243                         iput(dir);
 244                         return -EACCES;
 245                 }
 246                 if (IS_RDONLY(dir)) {
 247                         iput(dir);
 248                         return -EROFS;
 249                 }
 250                 return dir->i_op->create(dir,basename,namelen,mode,res_inode);
 251         }
 252         if (flag & O_EXCL) {
 253                 iput(dir);
 254                 iput(inode);
 255                 return -EEXIST;
 256         }
 257         if (error = follow_link(dir,inode,flag,mode,&inode))
 258                 return error;
 259         if (S_ISDIR(inode->i_mode) && (flag & 2)) {
 260                 iput(inode);
 261                 return -EPERM;
 262         }
 263         if (!permission(inode,ACC_MODE(flag))) {
 264                 iput(inode);
 265                 return -EACCES;
 266         }
 267         if (S_ISBLK(inode->i_mode) || S_ISCHR(inode->i_mode)) {
 268                 if (IS_NODEV(inode)) {
 269                         iput(inode);
 270                         return -EACCES;
 271                 }
 272         } else {
 273                 if (IS_RDONLY(inode) && (flag & 2)) {
 274                         iput(inode);
 275                         return -EROFS;
 276                 }
 277         }
 278         if ((inode->i_count > 1) && (flag & 2))
 279                 for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
 280                         if (!*p)
 281                                 continue;
 282                         if (inode == (*p)->executable) {
 283                                 iput(inode);
 284                                 return -ETXTBSY;
 285                         }
 286                         for (i=0; i < (*p)->numlibraries; i++)
 287                                 if (inode == (*p)->libraries[i].library) {
 288                                         iput(inode);
 289                                         return -ETXTBSY;
 290                                 }
 291                 }
 292         *res_inode = inode;
 293         return 0;
 294 }
 295 
 296 int do_mknod(const char * filename, int mode, dev_t dev)
     /*  */
 297 {
 298         const char * basename;
 299         int namelen, error;
 300         struct inode * dir;
 301 
 302         error = dir_namei(filename,&namelen,&basename, NULL, &dir);
 303         if (error)
 304                 return error;
 305         if (!namelen) {
 306                 iput(dir);
 307                 return -ENOENT;
 308         }
 309         if (IS_RDONLY(dir)) {
 310                 iput(dir);
 311                 return -EROFS;
 312         }
 313         if (!permission(dir,MAY_WRITE)) {
 314                 iput(dir);
 315                 return -EACCES;
 316         }
 317         if (!dir->i_op || !dir->i_op->mknod) {
 318                 iput(dir);
 319                 return -EPERM;
 320         }
 321         return dir->i_op->mknod(dir,basename,namelen,mode,dev);
 322 }
 323 
 324 int sys_mknod(const char * filename, int mode, dev_t dev)
     /*  */
 325 {
 326         if (S_ISFIFO(mode) || suser())
 327                 return do_mknod(filename,mode,dev);
 328         return -EPERM;
 329 }
 330 
 331 int sys_mkdir(const char * pathname, int mode)
     /*  */
 332 {
 333         const char * basename;
 334         int namelen, error;
 335         struct inode * dir;
 336 
 337         error = dir_namei(pathname,&namelen,&basename,NULL,&dir);
 338         if (error)
 339                 return error;
 340         if (!namelen) {
 341                 iput(dir);
 342                 return -ENOENT;
 343         }
 344         if (IS_RDONLY(dir)) {
 345                 iput(dir);
 346                 return -EROFS;
 347         }
 348         if (!permission(dir,MAY_WRITE)) {
 349                 iput(dir);
 350                 return -EACCES;
 351         }
 352         if (!dir->i_op || !dir->i_op->mkdir) {
 353                 iput(dir);
 354                 return -EPERM;
 355         }
 356         return dir->i_op->mkdir(dir,basename,namelen,mode);
 357 }
 358 
 359 int sys_rmdir(const char * name)
     /*  */
 360 {
 361         const char * basename;
 362         int namelen, error;
 363         struct inode * dir;
 364 
 365         error = dir_namei(name,&namelen,&basename,NULL,&dir);
 366         if (error)
 367                 return error;
 368         if (!namelen) {
 369                 iput(dir);
 370                 return -ENOENT;
 371         }
 372         if (IS_RDONLY(dir)) {
 373                 iput(dir);
 374                 return -EROFS;
 375         }
 376         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 377                 iput(dir);
 378                 return -EACCES;
 379         }
 380         if (!dir->i_op || !dir->i_op->rmdir) {
 381                 iput(dir);
 382                 return -EPERM;
 383         }
 384         return dir->i_op->rmdir(dir,basename,namelen);
 385 }
 386 
 387 int sys_unlink(const char * name)
     /*  */
 388 {
 389         const char * basename;
 390         int namelen, error;
 391         struct inode * dir;
 392 
 393         error = dir_namei(name,&namelen,&basename,NULL,&dir);
 394         if (error)
 395                 return error;
 396         if (!namelen) {
 397                 iput(dir);
 398                 return -EPERM;
 399         }
 400         if (IS_RDONLY(dir)) {
 401                 iput(dir);
 402                 return -EROFS;
 403         }
 404         if (!permission(dir,MAY_WRITE | MAY_EXEC)) {
 405                 iput(dir);
 406                 return -EACCES;
 407         }
 408         if (!dir->i_op || !dir->i_op->unlink) {
 409                 iput(dir);
 410                 return -EPERM;
 411         }
 412         return dir->i_op->unlink(dir,basename,namelen);
 413 }
 414 
 415 int sys_symlink(const char * oldname, const char * newname)
     /*  */
 416 {
 417         struct inode * dir;
 418         const char * basename;
 419         int namelen, error;
 420 
 421         error = dir_namei(newname,&namelen,&basename,NULL,&dir);
 422         if (error)
 423                 return error;
 424         if (!namelen) {
 425                 iput(dir);
 426                 return -ENOENT;
 427         }
 428         if (IS_RDONLY(dir)) {
 429                 iput(dir);
 430                 return -EROFS;
 431         }
 432         if (!permission(dir,MAY_WRITE)) {
 433                 iput(dir);
 434                 return -EACCES;
 435         }
 436         if (!dir->i_op || !dir->i_op->symlink) {
 437                 iput(dir);
 438                 return -EPERM;
 439         }
 440         return dir->i_op->symlink(dir,basename,namelen,oldname);
 441 }
 442 
 443 int sys_link(const char * oldname, const char * newname)
     /*  */
 444 {
 445         struct inode * oldinode, * dir;
 446         const char * basename;
 447         int namelen, error;
 448 
 449         error = namei(oldname, &oldinode);
 450         if (error)
 451                 return error;
 452         error = dir_namei(newname,&namelen,&basename,NULL,&dir);
 453         if (error) {
 454                 iput(oldinode);
 455                 return error;
 456         }
 457         if (!namelen) {
 458                 iput(oldinode);
 459                 iput(dir);
 460                 return -EPERM;
 461         }
 462         if (IS_RDONLY(dir)) {
 463                 iput(oldinode);
 464                 iput(dir);
 465                 return -EROFS;
 466         }
 467         if (dir->i_dev != oldinode->i_dev) {
 468                 iput(dir);
 469                 iput(oldinode);
 470                 return -EXDEV;
 471         }
 472         if (!permission(dir,MAY_WRITE)) {
 473                 iput(dir);
 474                 iput(oldinode);
 475                 return -EACCES;
 476         }
 477         if (!dir->i_op || !dir->i_op->link) {
 478                 iput(dir);
 479                 iput(oldinode);
 480                 return -EPERM;
 481         }
 482         return dir->i_op->link(oldinode, dir, basename, namelen);
 483 }
 484 
 485 int sys_rename(const char * oldname, const char * newname)
     /*  */
 486 {
 487         struct inode * old_dir, * new_dir;
 488         const char * old_base, * new_base;
 489         int old_len, new_len, error;
 490 
 491         error = dir_namei(oldname,&old_len,&old_base,NULL,&old_dir);
 492         if (error)
 493                 return error;
 494         if (!permission(old_dir,MAY_WRITE)) {
 495                 iput(old_dir);
 496                 return -EACCES;
 497         }
 498         if (!old_len || (get_fs_byte(old_base) == '.' &&
 499             (old_len == 1 || (get_fs_byte(old_base+1) == '.' &&
 500              old_len == 2)))) {
 501                 iput(old_dir);
 502                 return -EPERM;
 503         }
 504         error = dir_namei(newname,&new_len,&new_base,NULL,&new_dir);
 505         if (error) {
 506                 iput(old_dir);
 507                 return error;
 508         }
 509         if (!permission(new_dir,MAY_WRITE)) {
 510                 iput(old_dir);
 511                 iput(new_dir);
 512                 return -EACCES;
 513         }
 514         if (!new_len || (get_fs_byte(new_base) == '.' &&
 515             (new_len == 1 || (get_fs_byte(new_base+1) == '.' &&
 516              new_len == 2)))) {
 517                 iput(old_dir);
 518                 iput(new_dir);
 519                 return -EPERM;
 520         }
 521         if (new_dir->i_dev != old_dir->i_dev) {
 522                 iput(old_dir);
 523                 iput(new_dir);
 524                 return -EXDEV;
 525         }
 526         if (IS_RDONLY(new_dir) || IS_RDONLY(old_dir)) {
 527                 iput(old_dir);
 528                 iput(new_dir);
 529                 return -EROFS;
 530         }
 531         if (!old_dir->i_op || !old_dir->i_op->rename) {
 532                 iput(old_dir);
 533                 iput(new_dir);
 534                 return -EPERM;
 535         }
 536         return old_dir->i_op->rename(old_dir, old_base, old_len, 
 537                 new_dir, new_base, new_len);
 538 }
/* */
root/fs/namei.c

DEFINITIONS
