linux/fs/readdir.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/readdir.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 */

#include <linux/stddef.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/time.h>
#include <linux/mm.h>
#include <linux/errno.h>
#include <linux/stat.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/fsnotify.h>
#include <linux/dirent.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/unistd.h>
#include <linux/compat.h>
#include <linux/uaccess.h>

/*
 * Some filesystems were never converted to '->iterate_shared()'
 * and their directory iterators want the inode lock held for
 * writing. This wrapper allows for converting from the shared
 * semantics to the exclusive inode use.
 */
int wrap_directory_iterator(struct file *file,
			    struct dir_context *ctx,
			    int (*iter)(struct file *, struct dir_context *))
{ … }
EXPORT_SYMBOL(…);

/*
 * Note the "unsafe_put_user()" semantics: we goto a
 * label for errors.
 */
#define unsafe_copy_dirent_name(_dst, _src, _len, label) …


int iterate_dir(struct file *file, struct dir_context *ctx)
{ … }
EXPORT_SYMBOL(…);

/*
 * POSIX says that a dirent name cannot contain NULL or a '/'.
 *
 * It's not 100% clear what we should really do in this case.
 * The filesystem is clearly corrupted, but returning a hard
 * error means that you now don't see any of the other names
 * either, so that isn't a perfect alternative.
 *
 * And if you return an error, what error do you use? Several
 * filesystems seem to have decided on EUCLEAN being the error
 * code for EFSCORRUPTED, and that may be the error to use. Or
 * just EIO, which is perhaps more obvious to users.
 *
 * In order to see the other file names in the directory, the
 * caller might want to make this a "soft" error: skip the
 * entry, and return the error at the end instead.
 *
 * Note that this should likely do a "memchr(name, 0, len)"
 * check too, since that would be filesystem corruption as
 * well. However, that case can't actually confuse user space,
 * which has to do a strlen() on the name anyway to find the
 * filename length, and the above "soft error" worry means
 * that it's probably better left alone until we have that
 * issue clarified.
 *
 * Note the PATH_MAX check - it's arbitrary but the real
 * kernel limit on a possible path component, not NAME_MAX,
 * which is the technical standard limit.
 */
static int verify_dirent_name(const char *name, int len)
{ … }

/*
 * Traditional linux readdir() handling..
 *
 * "count=1" is a special case, meaning that the buffer is one
 * dirent-structure in size and that the code can't handle more
 * anyway. Thus the special "fillonedir()" function for that
 * case (the low-level handlers don't need to care about this).
 */

#ifdef __ARCH_WANT_OLD_READDIR

struct old_linux_dirent { … };

struct readdir_callback { … };

static bool fillonedir(struct dir_context *ctx, const char *name, int namlen,
		      loff_t offset, u64 ino, unsigned int d_type)
{ … }

SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
		struct old_linux_dirent __user *, dirent, unsigned int, count)
{ … }

#endif /* __ARCH_WANT_OLD_READDIR */

/*
 * New, all-improved, singing, dancing, iBCS2-compliant getdents()
 * interface. 
 */
struct linux_dirent { … };

struct getdents_callback { … };

static bool filldir(struct dir_context *ctx, const char *name, int namlen,
		   loff_t offset, u64 ino, unsigned int d_type)
{ … }

SYSCALL_DEFINE3(getdents, unsigned int, fd,
		struct linux_dirent __user *, dirent, unsigned int, count)
{ … }

struct getdents_callback64 { … };

static bool filldir64(struct dir_context *ctx, const char *name, int namlen,
		     loff_t offset, u64 ino, unsigned int d_type)
{ … }

SYSCALL_DEFINE3(getdents64, unsigned int, fd,
		struct linux_dirent64 __user *, dirent, unsigned int, count)
{ … }

#ifdef CONFIG_COMPAT
struct compat_old_linux_dirent { … };

struct compat_readdir_callback { … };

static bool compat_fillonedir(struct dir_context *ctx, const char *name,
			     int namlen, loff_t offset, u64 ino,
			     unsigned int d_type)
{ … }

COMPAT_SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
		struct compat_old_linux_dirent __user *, dirent, unsigned int, count)
{ … }

struct compat_linux_dirent { … };

struct compat_getdents_callback { … };

static bool compat_filldir(struct dir_context *ctx, const char *name, int namlen,
		loff_t offset, u64 ino, unsigned int d_type)
{ … }

COMPAT_SYSCALL_DEFINE3(getdents, unsigned int, fd,
		struct compat_linux_dirent __user *, dirent, unsigned int, count)
{ … }
#endif