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 
iterate_dir(struct file * file,struct dir_context * ctx)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  */
verify_dirent_name(const char * name,int len)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 
fillonedir(struct dir_context * ctx,const char * name,int namlen,loff_t offset,u64 ino,unsigned int d_type)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 
SYSCALL_DEFINE3(old_readdir,unsigned int,fd,struct old_linux_dirent __user *,dirent,unsigned int,count)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 
filldir(struct dir_context * ctx,const char * name,int namlen,loff_t offset,u64 ino,unsigned int d_type)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 
SYSCALL_DEFINE3(getdents,unsigned int,fd,struct linux_dirent __user *,dirent,unsigned int,count)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 
filldir64(struct dir_context * ctx,const char * name,int namlen,loff_t offset,u64 ino,unsigned int d_type)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 
SYSCALL_DEFINE3(getdents64,unsigned int,fd,struct linux_dirent64 __user *,dirent,unsigned int,count)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 
compat_fillonedir(struct dir_context * ctx,const char * name,int namlen,loff_t offset,u64 ino,unsigned int d_type)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 
COMPAT_SYSCALL_DEFINE3(old_readdir,unsigned int,fd,struct compat_old_linux_dirent __user *,dirent,unsigned int,count)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 
compat_filldir(struct dir_context * ctx,const char * name,int namlen,loff_t offset,u64 ino,unsigned int d_type)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 
COMPAT_SYSCALL_DEFINE3(getdents,unsigned int,fd,struct compat_linux_dirent __user *,dirent,unsigned int,count)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
553