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         buf->result = verify_dirent_name(name, namlen);
 154         if (buf->result < 0)
 155                 return buf->result;
 156         d_ino = ino;
 157         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 158                 buf->result = -EOVERFLOW;
 159                 return -EOVERFLOW;
 160         }
 161         buf->result++;
 162         dirent = buf->dirent;
 163         if (!user_write_access_begin(dirent,
 164                         (unsigned long)(dirent->d_name + namlen + 1) -
 165                                 (unsigned long)dirent))
 166                 goto efault;
 167         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 168         unsafe_put_user(offset, &dirent->d_offset, efault_end);
 169         unsafe_put_user(namlen, &dirent->d_namlen, efault_end);
 170         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 171         user_write_access_end();
 172         return 0;
 173 efault_end:
 174         user_write_access_end();
 175 efault:
 176         buf->result = -EFAULT;
 177         return -EFAULT;
 178 }
 179
 180 SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 181                 struct old_linux_dirent __user *, dirent, unsigned int, count)
 182 {
 183         int error;
 184         struct fd f = fdget_pos(fd);
 185         struct readdir_callback buf = {
 186                 .ctx.actor = fillonedir,
 187                 .dirent = dirent
 188         };
 189
 190         if (!f.file)
 191                 return -EBADF;
 192
 193         error = iterate_dir(f.file, &buf.ctx);
 194         if (buf.result)
 195                 error = buf.result;
 196
 197         fdput_pos(f);
 198         return error;
 199 }
 200
 201 #endif /* __ARCH_WANT_OLD_READDIR */
 202
 203 /*
 204  * New, all-improved, singing, dancing, iBCS2-compliant getdents()
 205  * interface.
 206  */
 207 struct linux_dirent {
 208         unsigned long   d_ino;
 209         unsigned long   d_off;
 210         unsigned short  d_reclen;
 211         char            d_name[1];
 212 };
 213
 214 struct getdents_callback {
 215         struct dir_context ctx;
 216         struct linux_dirent __user * current_dir;
 217         int prev_reclen;
 218         int count;
 219         int error;
 220 };
 221
 222 static int filldir(struct dir_context *ctx, const char *name, int namlen,
 223                    loff_t offset, u64 ino, unsigned int d_type)
 224 {
 225         struct linux_dirent __user *dirent, *prev;
 226         struct getdents_callback *buf =
 227                 container_of(ctx, struct getdents_callback, ctx);
 228         unsigned long d_ino;
 229         int reclen = ALIGN(offsetof(struct linux_dirent, d_name) + namlen + 2,
 230                 sizeof(long));
 231         int prev_reclen;
 232
 233         buf->error = verify_dirent_name(name, namlen);
 234         if (unlikely(buf->error))
 235                 return buf->error;
 236         buf->error = -EINVAL;   /* only used if we fail.. */
 237         if (reclen > buf->count)
 238                 return -EINVAL;
 239         d_ino = ino;
 240         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 241                 buf->error = -EOVERFLOW;
 242                 return -EOVERFLOW;
 243         }
 244         prev_reclen = buf->prev_reclen;
 245         if (prev_reclen && signal_pending(current))
 246                 return -EINTR;
 247         dirent = buf->current_dir;
 248         prev = (void __user *) dirent - prev_reclen;
 249         if (!user_write_access_begin(prev, reclen + prev_reclen))
 250                 goto efault;
 251
 252         /* This might be 'dirent->d_off', but if so it will get overwritten */
 253         unsafe_put_user(offset, &prev->d_off, efault_end);
 254         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 255         unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 256         unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
 257         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 258         user_write_access_end();
 259
 260         buf->current_dir = (void __user *)dirent + reclen;
 261         buf->prev_reclen = reclen;
 262         buf->count -= reclen;
 263         return 0;
 264 efault_end:
 265         user_write_access_end();
 266 efault:
 267         buf->error = -EFAULT;
 268         return -EFAULT;
 269 }
 270
 271 SYSCALL_DEFINE3(getdents, unsigned int, fd,
 272                 struct linux_dirent __user *, dirent, unsigned int, count)
 273 {
 274         struct fd f;
 275         struct getdents_callback buf = {
 276                 .ctx.actor = filldir,
 277                 .count = count,
 278                 .current_dir = dirent
 279         };
 280         int error;
 281
 282         f = fdget_pos(fd);
 283         if (!f.file)
 284                 return -EBADF;
 285
 286         error = iterate_dir(f.file, &buf.ctx);
 287         if (error >= 0)
 288                 error = buf.error;
 289         if (buf.prev_reclen) {
 290                 struct linux_dirent __user * lastdirent;
 291                 lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;
 292
 293                 if (put_user(buf.ctx.pos, &lastdirent->d_off))
 294                         error = -EFAULT;
 295                 else
 296                         error = count - buf.count;
 297         }
 298         fdput_pos(f);
 299         return error;
 300 }
 301
 302 struct getdents_callback64 {
 303         struct dir_context ctx;
 304         struct linux_dirent64 __user * current_dir;
 305         int prev_reclen;
 306         int count;
 307         int error;
 308 };
 309
 310 static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 311                      loff_t offset, u64 ino, unsigned int d_type)
 312 {
 313         struct linux_dirent64 __user *dirent, *prev;
 314         struct getdents_callback64 *buf =
 315                 container_of(ctx, struct getdents_callback64, ctx);
 316         int reclen = ALIGN(offsetof(struct linux_dirent64, d_name) + namlen + 1,
 317                 sizeof(u64));
 318         int prev_reclen;
 319
 320         buf->error = verify_dirent_name(name, namlen);
 321         if (unlikely(buf->error))
 322                 return buf->error;
 323         buf->error = -EINVAL;   /* only used if we fail.. */
 324         if (reclen > buf->count)
 325                 return -EINVAL;
 326         prev_reclen = buf->prev_reclen;
 327         if (prev_reclen && signal_pending(current))
 328                 return -EINTR;
 329         dirent = buf->current_dir;
 330         prev = (void __user *)dirent - prev_reclen;
 331         if (!user_write_access_begin(prev, reclen + prev_reclen))
 332                 goto efault;
 333
 334         /* This might be 'dirent->d_off', but if so it will get overwritten */
 335         unsafe_put_user(offset, &prev->d_off, efault_end);
 336         unsafe_put_user(ino, &dirent->d_ino, efault_end);
 337         unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 338         unsafe_put_user(d_type, &dirent->d_type, efault_end);
 339         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 340         user_write_access_end();
 341
 342         buf->prev_reclen = reclen;
 343         buf->current_dir = (void __user *)dirent + reclen;
 344         buf->count -= reclen;
 345         return 0;
 346
 347 efault_end:
 348         user_write_access_end();
 349 efault:
 350         buf->error = -EFAULT;
 351         return -EFAULT;
 352 }
 353
 354 SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 355                 struct linux_dirent64 __user *, dirent, unsigned int, count)
 356 {
 357         struct fd f;
 358         struct getdents_callback64 buf = {
 359                 .ctx.actor = filldir64,
 360                 .count = count,
 361                 .current_dir = dirent
 362         };
 363         int error;
 364
 365         f = fdget_pos(fd);
 366         if (!f.file)
 367                 return -EBADF;
 368
 369         error = iterate_dir(f.file, &buf.ctx);
 370         if (error >= 0)
 371                 error = buf.error;
 372         if (buf.prev_reclen) {
 373                 struct linux_dirent64 __user * lastdirent;
 374                 typeof(lastdirent->d_off) d_off = buf.ctx.pos;
 375
 376                 lastdirent = (void __user *) buf.current_dir - buf.prev_reclen;
 377                 if (put_user(d_off, &lastdirent->d_off))
 378                         error = -EFAULT;
 379                 else
 380                         error = count - buf.count;
 381         }
 382         fdput_pos(f);
 383         return error;
 384 }
 385
 386 #ifdef CONFIG_COMPAT
 387 struct compat_old_linux_dirent {
 388         compat_ulong_t  d_ino;
 389         compat_ulong_t  d_offset;
 390         unsigned short  d_namlen;
 391         char            d_name[1];
 392 };
 393
 394 struct compat_readdir_callback {
 395         struct dir_context ctx;
 396         struct compat_old_linux_dirent __user *dirent;
 397         int result;
 398 };
 399
 400 static int compat_fillonedir(struct dir_context *ctx, const char *name,
 401                              int namlen, loff_t offset, u64 ino,
 402                              unsigned int d_type)
 403 {
 404         struct compat_readdir_callback *buf =
 405                 container_of(ctx, struct compat_readdir_callback, ctx);
 406         struct compat_old_linux_dirent __user *dirent;
 407         compat_ulong_t d_ino;
 408
 409         if (buf->result)
 410                 return -EINVAL;
 411         buf->result = verify_dirent_name(name, namlen);
 412         if (buf->result < 0)
 413                 return buf->result;
 414         d_ino = ino;
 415         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 416                 buf->result = -EOVERFLOW;
 417                 return -EOVERFLOW;
 418         }
 419         buf->result++;
 420         dirent = buf->dirent;
 421         if (!user_write_access_begin(dirent,
 422                         (unsigned long)(dirent->d_name + namlen + 1) -
 423                                 (unsigned long)dirent))
 424                 goto efault;
 425         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 426         unsafe_put_user(offset, &dirent->d_offset, efault_end);
 427         unsafe_put_user(namlen, &dirent->d_namlen, efault_end);
 428         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 429         user_write_access_end();
 430         return 0;
 431 efault_end:
 432         user_write_access_end();
 433 efault:
 434         buf->result = -EFAULT;
 435         return -EFAULT;
 436 }
 437
 438 COMPAT_SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 439                 struct compat_old_linux_dirent __user *, dirent, unsigned int, count)
 440 {
 441         int error;
 442         struct fd f = fdget_pos(fd);
 443         struct compat_readdir_callback buf = {
 444                 .ctx.actor = compat_fillonedir,
 445                 .dirent = dirent
 446         };
 447
 448         if (!f.file)
 449                 return -EBADF;
 450
 451         error = iterate_dir(f.file, &buf.ctx);
 452         if (buf.result)
 453                 error = buf.result;
 454
 455         fdput_pos(f);
 456         return error;
 457 }
 458
 459 struct compat_linux_dirent {
 460         compat_ulong_t  d_ino;
 461         compat_ulong_t  d_off;
 462         unsigned short  d_reclen;
 463         char            d_name[1];
 464 };
 465
 466 struct compat_getdents_callback {
 467         struct dir_context ctx;
 468         struct compat_linux_dirent __user *current_dir;
 469         int prev_reclen;
 470         int count;
 471         int error;
 472 };
 473
 474 static int compat_filldir(struct dir_context *ctx, const char *name, int namlen,
 475                 loff_t offset, u64 ino, unsigned int d_type)
 476 {
 477         struct compat_linux_dirent __user *dirent, *prev;
 478         struct compat_getdents_callback *buf =
 479                 container_of(ctx, struct compat_getdents_callback, ctx);
 480         compat_ulong_t d_ino;
 481         int reclen = ALIGN(offsetof(struct compat_linux_dirent, d_name) +
 482                 namlen + 2, sizeof(compat_long_t));
 483         int prev_reclen;
 484
 485         buf->error = verify_dirent_name(name, namlen);
 486         if (unlikely(buf->error))
 487                 return buf->error;
 488         buf->error = -EINVAL;   /* only used if we fail.. */
 489         if (reclen > buf->count)
 490                 return -EINVAL;
 491         d_ino = ino;
 492         if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 493                 buf->error = -EOVERFLOW;
 494                 return -EOVERFLOW;
 495         }
 496         prev_reclen = buf->prev_reclen;
 497         if (prev_reclen && signal_pending(current))
 498                 return -EINTR;
 499         dirent = buf->current_dir;
 500         prev = (void __user *) dirent - prev_reclen;
 501         if (!user_write_access_begin(prev, reclen + prev_reclen))
 502                 goto efault;
 503
 504         unsafe_put_user(offset, &prev->d_off, efault_end);
 505         unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 506         unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 507         unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
 508         unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
 509         user_write_access_end();
 510
 511         buf->prev_reclen = reclen;
 512         buf->current_dir = (void __user *)dirent + reclen;
 513         buf->count -= reclen;
 514         return 0;
 515 efault_end:
 516         user_write_access_end();
 517 efault:
 518         buf->error = -EFAULT;
 519         return -EFAULT;
 520 }
 521
 522 COMPAT_SYSCALL_DEFINE3(getdents, unsigned int, fd,
 523                 struct compat_linux_dirent __user *, dirent, unsigned int, count)
 524 {
 525         struct fd f;
 526         struct compat_getdents_callback buf = {
 527                 .ctx.actor = compat_filldir,
 528                 .current_dir = dirent,
 529                 .count = count
 530         };
 531         int error;
 532
 533         f = fdget_pos(fd);
 534         if (!f.file)
 535                 return -EBADF;
 536
 537         error = iterate_dir(f.file, &buf.ctx);
 538         if (error >= 0)
 539                 error = buf.error;
 540         if (buf.prev_reclen) {
 541                 struct compat_linux_dirent __user * lastdirent;
 542                 lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;
 543
 544                 if (put_user(buf.ctx.pos, &lastdirent->d_off))
 545                         error = -EFAULT;
 546                 else
 547                         error = count - buf.count;
 548         }
 549         fdput_pos(f);
 550         return error;
 551 }
 552 #endif