fs/readdir.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/readdir.c
   4  *
   5  *  Copyright (C) 1995  Linus Torvalds
   6  */
   7
   8 #include <linux/stddef.h>
   9 #include <linux/kernel.h>
  10 #include <linux/export.h>
  11 #include <linux/time.h>
  12 #include <linux/mm.h>
  13 #include <linux/errno.h>
  14 #include <linux/stat.h>
  15 #include <linux/file.h>
  16 #include <linux/fs.h>
  17 #include <linux/fsnotify.h>
  18 #include <linux/dirent.h>
  19 #include <linux/security.h>
  20 #include <linux/syscalls.h>
  21 #include <linux/unistd.h>
  22 #include <linux/compat.h>
  23 #include <linux/uaccess.h>
  24
  25 #include <asm/unaligned.h>
  26
  27 /*
  28  * Note the "unsafe_put_user() semantics: we goto a
  29  * label for errors.
  30  */
  31 #define unsafe_copy_dirent_name(_dst, _src, _len, label) do {   \
  32         char __user *dst = (_dst);                              \
  33         const char *src = (_src);                               \
  34         size_t len = (_len);                                    \
  35         unsafe_put_user(0, dst+len, label);                     \
  36         unsafe_copy_to_user(dst, src, len, label);              \
  37 } while (0)
  38
  39
  40 int iterate_dir(struct file *file, struct dir_context *ctx)
  41 {
  42         struct inode *inode = file_inode(file);
  43         bool shared = false;
  44         int res = -ENOTDIR;
  45         if (file->f_op->iterate_shared)
  46                 shared = true;
  47         else if (!file->f_op->iterate)
  48                 goto out;
  49
  50         res = security_file_permission(file, MAY_READ);
  51         if (res)
  52                 goto out;
  53
  54         if (shared)
  55                 res = down_read_killable(&inode->i_rwsem);
  56         else
  57                 res = down_write_killable(&inode->i_rwsem);
  58         if (res)
  59                 goto out;
  60
  61         res = -ENOENT;
  62         if (!IS_DEADDIR(inode)) {
  63                 ctx->pos = file->f_pos;
  64                 if (shared)
  65                         res = file->f_op->iterate_shared(file, ctx);
  66                 else
  67                         res = file->f_op->iterate(file, ctx);
  68                 file->f_pos = ctx->pos;
  69                 fsnotify_access(file);
  70                 file_accessed(file);
  71         }
  72         if (shared)
  73                 inode_unlock_shared(inode);
  74         else
  75                 inode_unlock(inode);
  76 out:
  77         return res;
  78 }
  79 EXPORT_SYMBOL(iterate_dir);
  80
  81 /*
  82  * POSIX says that a dirent name cannot contain NULL or a '/'.
  83  *
  84  * It's not 100% clear what we should really do in this case.
  85  * The filesystem is clearly corrupted, but returning a hard
  86  * error means that you now don't see any of the other names
  87  * either, so that isn't a perfect alternative.
  88  *
  89  * And if you return an error, what error do you use? Several
  90  * filesystems seem to have decided on EUCLEAN being the error
  91  * code for EFSCORRUPTED, and that may be the error to use. Or
  92  * just EIO, which is perhaps more obvious to users.
  93  *
  94  * In order to see the other file names in the directory, the
  95  * caller might want to make this a "soft" error: skip the
  96  * entry, and return the error at the end instead.
  97  *
  98  * Note that this should likely do a "memchr(name, 0, len)"
  99  * check too, since that would be filesystem corruption as
 100  * well. However, that case can't actually confuse user space,
 101  * which has to do a strlen() on the name anyway to find the
 102  * filename length, and the above "soft error" worry means
 103  * that it's probably better left alone until we have that
 104  * issue clarified.
 105  *
 106  * Note the PATH_MAX check - it's arbitrary but the real
 107  * kernel limit on a possible path component, not NAME_MAX,
 108  * which is the technical standard limit.
 109  */
 110 static int verify_dirent_name(const char *name, int len)
 111 {
 112         if (len <= 0 || len >= PATH_MAX)
 113                 return -EIO;
 114         if (memchr(name, '/', len))
 115                 return -EIO;
 116         return 0;
 117 }
 118
 119 /*
 120  * Traditional linux readdir() handling..
 121  *
 122  * "count=1" is a special case, meaning that the buffer is one
 123  * dirent-structure in size and that the code can't handle more
 124  * anyway. Thus the special "fillonedir()" function for that
 125  * case (the low-level handlers don't need to care about this).
 126  */
 127
 128 #ifdef __ARCH_WANT_OLD_READDIR
 129
 130 struct old_linux_dirent {
 131         unsigned long   d_ino;
 132         unsigned long   d_offset;
 133         unsigned short  d_namlen;
 134         char            d_name[1];
 135 };
 136
 137 struct readdir_callback {
 138         struct dir_context ctx;
 139         struct old_linux_dirent __user * dirent;
 140         int result;
 141 };
 142
 143 static int fillonedir(struct dir_context *ctx, const char *name, int namlen,
 144                       loff_t offset, u64 ino, unsigned int d_type)
 145 {
 146         struct readdir_callback *buf =
 147                 container_of(ctx, struct readdir_callback, ctx);
 148         struct old_linux_dirent __user * dirent;
 149         unsigned long d_ino;
 150
 151         if (buf->result)
 152                 return -EINVAL;
 153         d_ino = ino;
 154         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 155                 buf->result = -EOVERFLOW;
 156                 return -EOVERFLOW;
 157         }
 158         buf->result++;
 159         dirent = buf->dirent;
 160         if (!user_write_access_begin(dirent,
 161                         (unsigned long)(dirent->d_name + namlen + 1) -
 162                                 (unsigned long)dirent))
 163                 goto efault;
 164         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 165         unsafe_put_user(offset, &dirent->d_offset, efault_end);
 166         unsafe_put_user(namlen, &dirent->d_namlen, efault_end);
 167         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 168         user_write_access_end();
 169         return 0;
 170 efault_end:
 171         user_write_access_end();
 172 efault:
 173         buf->result = -EFAULT;
 174         return -EFAULT;
 175 }
 176
 177 SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 178                 struct old_linux_dirent __user *, dirent, unsigned int, count)
 179 {
 180         int error;
 181         struct fd f = fdget_pos(fd);
 182         struct readdir_callback buf = {
 183                 .ctx.actor = fillonedir,
 184                 .dirent = dirent
 185         };
 186
 187         if (!f.file)
 188                 return -EBADF;
 189
 190         error = iterate_dir(f.file, &buf.ctx);
 191         if (buf.result)
 192                 error = buf.result;
 193
 194         fdput_pos(f);
 195         return error;
 196 }
 197
 198 #endif /* __ARCH_WANT_OLD_READDIR */
 199
 200 /*
 201  * New, all-improved, singing, dancing, iBCS2-compliant getdents()
 202  * interface.
 203  */
 204 struct linux_dirent {
 205         unsigned long   d_ino;
 206         unsigned long   d_off;
 207         unsigned short  d_reclen;
 208         char            d_name[1];
 209 };
 210
 211 struct getdents_callback {
 212         struct dir_context ctx;
 213         struct linux_dirent __user * current_dir;
 214         int prev_reclen;
 215         int count;
 216         int error;
 217 };
 218
 219 static int filldir(struct dir_context *ctx, const char *name, int namlen,
 220                    loff_t offset, u64 ino, unsigned int d_type)
 221 {
 222         struct linux_dirent __user *dirent, *prev;
 223         struct getdents_callback *buf =
 224                 container_of(ctx, struct getdents_callback, ctx);
 225         unsigned long d_ino;
 226         int reclen = ALIGN(offsetof(struct linux_dirent, d_name) + namlen + 2,
 227                 sizeof(long));
 228         int prev_reclen;
 229
 230         buf->error = verify_dirent_name(name, namlen);
 231         if (unlikely(buf->error))
 232                 return buf->error;
 233         buf->error = -EINVAL;   /* only used if we fail.. */
 234         if (reclen > buf->count)
 235                 return -EINVAL;
 236         d_ino = ino;
 237         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 238                 buf->error = -EOVERFLOW;
 239                 return -EOVERFLOW;
 240         }
 241         prev_reclen = buf->prev_reclen;
 242         if (prev_reclen && signal_pending(current))
 243                 return -EINTR;
 244         dirent = buf->current_dir;
 245         prev = (void __user *) dirent - prev_reclen;
 246         if (!user_write_access_begin(prev, reclen + prev_reclen))
 247                 goto efault;
 248
 249         /* This might be 'dirent->d_off', but if so it will get overwritten */
 250         unsafe_put_user(offset, &prev->d_off, efault_end);
 251         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 252         unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 253         unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
 254         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 255         user_write_access_end();
 256
 257         buf->current_dir = (void __user *)dirent + reclen;
 258         buf->prev_reclen = reclen;
 259         buf->count -= reclen;
 260         return 0;
 261 efault_end:
 262         user_write_access_end();
 263 efault:
 264         buf->error = -EFAULT;
 265         return -EFAULT;
 266 }
 267
 268 SYSCALL_DEFINE3(getdents, unsigned int, fd,
 269                 struct linux_dirent __user *, dirent, unsigned int, count)
 270 {
 271         struct fd f;
 272         struct getdents_callback buf = {
 273                 .ctx.actor = filldir,
 274                 .count = count,
 275                 .current_dir = dirent
 276         };
 277         int error;
 278
 279         f = fdget_pos(fd);
 280         if (!f.file)
 281                 return -EBADF;
 282
 283         error = iterate_dir(f.file, &buf.ctx);
 284         if (error >= 0)
 285                 error = buf.error;
 286         if (buf.prev_reclen) {
 287                 struct linux_dirent __user * lastdirent;
 288                 lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;
 289
 290                 if (put_user(buf.ctx.pos, &lastdirent->d_off))
 291                         error = -EFAULT;
 292                 else
 293                         error = count - buf.count;
 294         }
 295         fdput_pos(f);
 296         return error;
 297 }
 298
 299 struct getdents_callback64 {
 300         struct dir_context ctx;
 301         struct linux_dirent64 __user * current_dir;
 302         int prev_reclen;
 303         int count;
 304         int error;
 305 };
 306
 307 static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 308                      loff_t offset, u64 ino, unsigned int d_type)
 309 {
 310         struct linux_dirent64 __user *dirent, *prev;
 311         struct getdents_callback64 *buf =
 312                 container_of(ctx, struct getdents_callback64, ctx);
 313         int reclen = ALIGN(offsetof(struct linux_dirent64, d_name) + namlen + 1,
 314                 sizeof(u64));
 315         int prev_reclen;
 316
 317         buf->error = verify_dirent_name(name, namlen);
 318         if (unlikely(buf->error))
 319                 return buf->error;
 320         buf->error = -EINVAL;   /* only used if we fail.. */
 321         if (reclen > buf->count)
 322                 return -EINVAL;
 323         prev_reclen = buf->prev_reclen;
 324         if (prev_reclen && signal_pending(current))
 325                 return -EINTR;
 326         dirent = buf->current_dir;
 327         prev = (void __user *)dirent - prev_reclen;
 328         if (!user_write_access_begin(prev, reclen + prev_reclen))
 329                 goto efault;
 330
 331         /* This might be 'dirent->d_off', but if so it will get overwritten */
 332         unsafe_put_user(offset, &prev->d_off, efault_end);
 333         unsafe_put_user(ino, &dirent->d_ino, efault_end);
 334         unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 335         unsafe_put_user(d_type, &dirent->d_type, efault_end);
 336         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 337         user_write_access_end();
 338
 339         buf->prev_reclen = reclen;
 340         buf->current_dir = (void __user *)dirent + reclen;
 341         buf->count -= reclen;
 342         return 0;
 343
 344 efault_end:
 345         user_write_access_end();
 346 efault:
 347         buf->error = -EFAULT;
 348         return -EFAULT;
 349 }
 350
 351 SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 352                 struct linux_dirent64 __user *, dirent, unsigned int, count)
 353 {
 354         struct fd f;
 355         struct getdents_callback64 buf = {
 356                 .ctx.actor = filldir64,
 357                 .count = count,
 358                 .current_dir = dirent
 359         };
 360         int error;
 361
 362         f = fdget_pos(fd);
 363         if (!f.file)
 364                 return -EBADF;
 365
 366         error = iterate_dir(f.file, &buf.ctx);
 367         if (error >= 0)
 368                 error = buf.error;
 369         if (buf.prev_reclen) {
 370                 struct linux_dirent64 __user * lastdirent;
 371                 typeof(lastdirent->d_off) d_off = buf.ctx.pos;
 372
 373                 lastdirent = (void __user *) buf.current_dir - buf.prev_reclen;
 374                 if (put_user(d_off, &lastdirent->d_off))
 375                         error = -EFAULT;
 376                 else
 377                         error = count - buf.count;
 378         }
 379         fdput_pos(f);
 380         return error;
 381 }
 382
 383 #ifdef CONFIG_COMPAT
 384 struct compat_old_linux_dirent {
 385         compat_ulong_t  d_ino;
 386         compat_ulong_t  d_offset;
 387         unsigned short  d_namlen;
 388         char            d_name[1];
 389 };
 390
 391 struct compat_readdir_callback {
 392         struct dir_context ctx;
 393         struct compat_old_linux_dirent __user *dirent;
 394         int result;
 395 };
 396
 397 static int compat_fillonedir(struct dir_context *ctx, const char *name,
 398                              int namlen, loff_t offset, u64 ino,
 399                              unsigned int d_type)
 400 {
 401         struct compat_readdir_callback *buf =
 402                 container_of(ctx, struct compat_readdir_callback, ctx);
 403         struct compat_old_linux_dirent __user *dirent;
 404         compat_ulong_t d_ino;
 405
 406         if (buf->result)
 407                 return -EINVAL;
 408         d_ino = ino;
 409         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 410                 buf->result = -EOVERFLOW;
 411                 return -EOVERFLOW;
 412         }
 413         buf->result++;
 414         dirent = buf->dirent;
 415         if (!user_write_access_begin(dirent,
 416                         (unsigned long)(dirent->d_name + namlen + 1) -
 417                                 (unsigned long)dirent))
 418                 goto efault;
 419         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 420         unsafe_put_user(offset, &dirent->d_offset, efault_end);
 421         unsafe_put_user(namlen, &dirent->d_namlen, efault_end);
 422         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 423         user_write_access_end();
 424         return 0;
 425 efault_end:
 426         user_write_access_end();
 427 efault:
 428         buf->result = -EFAULT;
 429         return -EFAULT;
 430 }
 431
 432 COMPAT_SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 433                 struct compat_old_linux_dirent __user *, dirent, unsigned int, count)
 434 {
 435         int error;
 436         struct fd f = fdget_pos(fd);
 437         struct compat_readdir_callback buf = {
 438                 .ctx.actor = compat_fillonedir,
 439                 .dirent = dirent
 440         };
 441
 442         if (!f.file)
 443                 return -EBADF;
 444
 445         error = iterate_dir(f.file, &buf.ctx);
 446         if (buf.result)
 447                 error = buf.result;
 448
 449         fdput_pos(f);
 450         return error;
 451 }
 452
 453 struct compat_linux_dirent {
 454         compat_ulong_t  d_ino;
 455         compat_ulong_t  d_off;
 456         unsigned short  d_reclen;
 457         char            d_name[1];
 458 };
 459
 460 struct compat_getdents_callback {
 461         struct dir_context ctx;
 462         struct compat_linux_dirent __user *current_dir;
 463         int prev_reclen;
 464         int count;
 465         int error;
 466 };
 467
 468 static int compat_filldir(struct dir_context *ctx, const char *name, int namlen,
 469                 loff_t offset, u64 ino, unsigned int d_type)
 470 {
 471         struct compat_linux_dirent __user *dirent, *prev;
 472         struct compat_getdents_callback *buf =
 473                 container_of(ctx, struct compat_getdents_callback, ctx);
 474         compat_ulong_t d_ino;
 475         int reclen = ALIGN(offsetof(struct compat_linux_dirent, d_name) +
 476                 namlen + 2, sizeof(compat_long_t));
 477         int prev_reclen;
 478
 479         buf->error = verify_dirent_name(name, namlen);
 480         if (unlikely(buf->error))
 481                 return buf->error;
 482         buf->error = -EINVAL;   /* only used if we fail.. */
 483         if (reclen > buf->count)
 484                 return -EINVAL;
 485         d_ino = ino;
 486         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 487                 buf->error = -EOVERFLOW;
 488                 return -EOVERFLOW;
 489         }
 490         prev_reclen = buf->prev_reclen;
 491         if (prev_reclen && signal_pending(current))
 492                 return -EINTR;
 493         dirent = buf->current_dir;
 494         prev = (void __user *) dirent - prev_reclen;
 495         if (!user_write_access_begin(prev, reclen + prev_reclen))
 496                 goto efault;
 497
 498         unsafe_put_user(offset, &prev->d_off, efault_end);
 499         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 500         unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 501         unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
 502         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 503         user_write_access_end();
 504
 505         buf->prev_reclen = reclen;
 506         buf->current_dir = (void __user *)dirent + reclen;
 507         buf->count -= reclen;
 508         return 0;
 509 efault_end:
 510         user_write_access_end();
 511 efault:
 512         buf->error = -EFAULT;
 513         return -EFAULT;
 514 }
 515
 516 COMPAT_SYSCALL_DEFINE3(getdents, unsigned int, fd,
 517                 struct compat_linux_dirent __user *, dirent, unsigned int, count)
 518 {
 519         struct fd f;
 520         struct compat_getdents_callback buf = {
 521                 .ctx.actor = compat_filldir,
 522                 .current_dir = dirent,
 523                 .count = count
 524         };
 525         int error;
 526
 527         f = fdget_pos(fd);
 528         if (!f.file)
 529                 return -EBADF;
 530
 531         error = iterate_dir(f.file, &buf.ctx);
 532         if (error >= 0)
 533                 error = buf.error;
 534         if (buf.prev_reclen) {
 535                 struct compat_linux_dirent __user * lastdirent;
 536                 lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;
 537
 538                 if (put_user(buf.ctx.pos, &lastdirent->d_off))
 539                         error = -EFAULT;
 540                 else
 541                         error = count - buf.count;
 542         }
 543         fdput_pos(f);
 544         return error;
 545 }
 546 #endif