freebsd-dev/sbin/fsck_msdosfs/dir.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2019 Google LLC
 * Copyright (C) 1995, 1996, 1997 Wolfgang Solfrank
 * Copyright (c) 1995 Martin Husemann
 * Some structure declaration borrowed from Paul Popelka
 * (paulp@uts.amdahl.com), see /sys/msdosfs/ for reference.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: dir.c,v 1.20 2006/06/05 16:51:18 christos Exp $");
static const char rcsid[] =
  "$FreeBSD$";
#endif /* not lint */

#include <assert.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <time.h>

#include <sys/param.h>

#include "ext.h"
#include "fsutil.h"

#define	SLOT_EMPTY	0x00		/* slot has never been used */
#define	SLOT_E5		0x05		/* the real value is 0xe5 */
#define	SLOT_DELETED	0xe5		/* file in this slot deleted */

#define	ATTR_NORMAL	0x00		/* normal file */
#define	ATTR_READONLY	0x01		/* file is readonly */
#define	ATTR_HIDDEN	0x02		/* file is hidden */
#define	ATTR_SYSTEM	0x04		/* file is a system file */
#define	ATTR_VOLUME	0x08		/* entry is a volume label */
#define	ATTR_DIRECTORY	0x10		/* entry is a directory name */
#define	ATTR_ARCHIVE	0x20		/* file is new or modified */

#define	ATTR_WIN95	0x0f		/* long name record */

/*
 * This is the format of the contents of the deTime field in the direntry
 * structure.
 * We don't use bitfields because we don't know how compilers for
 * arbitrary machines will lay them out.
 */
#define DT_2SECONDS_MASK	0x1F	/* seconds divided by 2 */
#define DT_2SECONDS_SHIFT	0
#define DT_MINUTES_MASK		0x7E0	/* minutes */
#define DT_MINUTES_SHIFT	5
#define DT_HOURS_MASK		0xF800	/* hours */
#define DT_HOURS_SHIFT		11

/*
 * This is the format of the contents of the deDate field in the direntry
 * structure.
 */
#define DD_DAY_MASK		0x1F	/* day of month */
#define DD_DAY_SHIFT		0
#define DD_MONTH_MASK		0x1E0	/* month */
#define DD_MONTH_SHIFT		5
#define DD_YEAR_MASK		0xFE00	/* year - 1980 */
#define DD_YEAR_SHIFT		9


/* dir.c */
static struct dosDirEntry *newDosDirEntry(void);
static void freeDosDirEntry(struct dosDirEntry *);
static struct dirTodoNode *newDirTodo(void);
static void freeDirTodo(struct dirTodoNode *);
static char *fullpath(struct dosDirEntry *);
static u_char calcShortSum(u_char *);
static int delete(struct fat_descriptor *, cl_t, int, cl_t, int, int);
static int removede(struct fat_descriptor *, u_char *, u_char *,
    cl_t, cl_t, cl_t, char *, int);
static int checksize(struct fat_descriptor *, u_char *, struct dosDirEntry *);
static int readDosDirSection(struct fat_descriptor *, struct dosDirEntry *);

/*
 * Manage free dosDirEntry structures.
 */
static struct dosDirEntry *freede;

static struct dosDirEntry *
newDosDirEntry(void)
{
	struct dosDirEntry *de;

	if (!(de = freede)) {
		if (!(de = malloc(sizeof *de)))
			return (NULL);
	} else
		freede = de->next;
	return de;
}

static void
freeDosDirEntry(struct dosDirEntry *de)
{
	de->next = freede;
	freede = de;
}

/*
 * The same for dirTodoNode structures.
 */
static struct dirTodoNode *freedt;

static struct dirTodoNode *
newDirTodo(void)
{
	struct dirTodoNode *dt;

	if (!(dt = freedt)) {
		if (!(dt = malloc(sizeof *dt)))
			return 0;
	} else
		freedt = dt->next;
	return dt;
}

static void
freeDirTodo(struct dirTodoNode *dt)
{
	dt->next = freedt;
	freedt = dt;
}

/*
 * The stack of unread directories
 */
static struct dirTodoNode *pendingDirectories = NULL;

/*
 * Return the full pathname for a directory entry.
 */
static char *
fullpath(struct dosDirEntry *dir)
{
	static char namebuf[MAXPATHLEN + 1];
	char *cp, *np;
	int nl;

	cp = namebuf + sizeof namebuf;
	*--cp = '\0';

	for(;;) {
		np = dir->lname[0] ? dir->lname : dir->name;
		nl = strlen(np);
		if (cp <= namebuf + 1 + nl) {
			*--cp = '?';
			break;
		}
		cp -= nl;
		memcpy(cp, np, nl);
		dir = dir->parent;
		if (!dir)
			break;
		*--cp = '/';
	}

	return cp;
}

/*
 * Calculate a checksum over an 8.3 alias name
 */
static inline u_char
calcShortSum(u_char *p)
{
	u_char sum = 0;
	int i;

	for (i = 0; i < 11; i++) {
		sum = (sum << 7)|(sum >> 1);	/* rotate right */
		sum += p[i];
	}

	return sum;
}

/*
 * Global variables temporarily used during a directory scan
 */
static char longName[DOSLONGNAMELEN] = "";
static u_char *buffer = NULL;
static u_char *delbuf = NULL;

static struct dosDirEntry *rootDir;
static struct dosDirEntry *lostDir;

/*
 * Init internal state for a new directory scan.
 */
int
resetDosDirSection(struct fat_descriptor *fat)
{
	int rootdir_size, cluster_size;
	int ret = FSOK;
	size_t len;
	struct bootblock *boot;

	boot = fat_get_boot(fat);

	rootdir_size = boot->bpbRootDirEnts * 32;
	cluster_size = boot->bpbSecPerClust * boot->bpbBytesPerSec;

	if ((buffer = malloc(len = MAX(rootdir_size, cluster_size))) == NULL) {
		perr("No space for directory buffer (%zu)", len);
		return FSFATAL;
	}

	if ((delbuf = malloc(len = cluster_size)) == NULL) {
		free(buffer);
		perr("No space for directory delbuf (%zu)", len);
		return FSFATAL;
	}

	if ((rootDir = newDosDirEntry()) == NULL) {
		free(buffer);
		free(delbuf);
		perr("No space for directory entry");
		return FSFATAL;
	}

	memset(rootDir, 0, sizeof *rootDir);
	if (boot->flags & FAT32) {
		if (!fat_is_cl_head(fat, boot->bpbRootClust)) {
			pfatal("Root directory doesn't start a cluster chain");
			return FSFATAL;
		}
		rootDir->head = boot->bpbRootClust;
	}

	return ret;
}

/*
 * Cleanup after a directory scan
 */
void
finishDosDirSection(void)
{
	struct dirTodoNode *p, *np;
	struct dosDirEntry *d, *nd;

	for (p = pendingDirectories; p; p = np) {
		np = p->next;
		freeDirTodo(p);
	}
	pendingDirectories = NULL;
	for (d = rootDir; d; d = nd) {
		if ((nd = d->child) != NULL) {
			d->child = 0;
			continue;
		}
		if (!(nd = d->next))
			nd = d->parent;
		freeDosDirEntry(d);
	}
	rootDir = lostDir = NULL;
	free(buffer);
	free(delbuf);
	buffer = NULL;
	delbuf = NULL;
}

/*
 * Delete directory entries between startcl, startoff and endcl, endoff.
 */
static int
delete(struct fat_descriptor *fat, cl_t startcl,
    int startoff, cl_t endcl, int endoff, int notlast)
{
	u_char *s, *e;
	off_t off;
	int clsz, fd;
	struct bootblock *boot;

	boot = fat_get_boot(fat);
	fd = fat_get_fd(fat);
	clsz = boot->bpbSecPerClust * boot->bpbBytesPerSec;

	s = delbuf + startoff;
	e = delbuf + clsz;
	while (fat_is_valid_cl(fat, startcl)) {
		if (startcl == endcl) {
			if (notlast)
				break;
			e = delbuf + endoff;
		}
		off = (startcl - CLUST_FIRST) * boot->bpbSecPerClust + boot->FirstCluster;

		off *= boot->bpbBytesPerSec;
		if (lseek(fd, off, SEEK_SET) != off) {
			perr("Unable to lseek to %" PRId64, off);
			return FSFATAL;
		}
		if (read(fd, delbuf, clsz) != clsz) {
			perr("Unable to read directory");
			return FSFATAL;
		}
		while (s < e) {
			*s = SLOT_DELETED;
			s += 32;
		}
		if (lseek(fd, off, SEEK_SET) != off) {
			perr("Unable to lseek to %" PRId64, off);
			return FSFATAL;
		}
		if (write(fd, delbuf, clsz) != clsz) {
			perr("Unable to write directory");
			return FSFATAL;
		}
		if (startcl == endcl)
			break;
		startcl = fat_get_cl_next(fat, startcl);
		s = delbuf;
	}
	return FSOK;
}

static int
removede(struct fat_descriptor *fat, u_char *start,
    u_char *end, cl_t startcl, cl_t endcl, cl_t curcl,
    char *path, int type)
{
	switch (type) {
	case 0:
		pwarn("Invalid long filename entry for %s\n", path);
		break;
	case 1:
		pwarn("Invalid long filename entry at end of directory %s\n",
		    path);
		break;
	case 2:
		pwarn("Invalid long filename entry for volume label\n");
		break;
	}
	if (ask(0, "Remove")) {
		if (startcl != curcl) {
			if (delete(fat,
				   startcl, start - buffer,
				   endcl, end - buffer,
				   endcl == curcl) == FSFATAL)
				return FSFATAL;
			start = buffer;
		}
		/* startcl is < CLUST_FIRST for !FAT32 root */
		if ((endcl == curcl) || (startcl < CLUST_FIRST))
			for (; start < end; start += 32)
				*start = SLOT_DELETED;
		return FSDIRMOD;
	}
	return FSERROR;
}

/*
 * Check an in-memory file entry
 */
static int
checksize(struct fat_descriptor *fat, u_char *p, struct dosDirEntry *dir)
{
	int ret = FSOK;
	size_t physicalSize;
	struct bootblock *boot;

	boot = fat_get_boot(fat);

	/*
	 * Check size on ordinary files
	 */
	if (dir->head == CLUST_FREE) {
		physicalSize = 0;
	} else {
		if (!fat_is_valid_cl(fat, dir->head))
			return FSERROR;
		ret = checkchain(fat, dir->head, &physicalSize);
		/*
		 * Upon return, physicalSize would hold the chain length
		 * that checkchain() was able to validate, but if the user
		 * refused the proposed repair, it would be unsafe to
		 * proceed with directory entry fix, so bail out in that
		 * case.
		 */
		if (ret == FSERROR) {
			return (FSERROR);
		}
		physicalSize *= boot->ClusterSize;
	}
	if (physicalSize < dir->size) {
		pwarn("size of %s is %u, should at most be %zu\n",
		      fullpath(dir), dir->size, physicalSize);
		if (ask(1, "Truncate")) {
			dir->size = physicalSize;
			p[28] = (u_char)physicalSize;
			p[29] = (u_char)(physicalSize >> 8);
			p[30] = (u_char)(physicalSize >> 16);
			p[31] = (u_char)(physicalSize >> 24);
			return FSDIRMOD;
		} else
			return FSERROR;
	} else if (physicalSize - dir->size >= boot->ClusterSize) {
		pwarn("%s has too many clusters allocated\n",
		      fullpath(dir));
		if (ask(1, "Drop superfluous clusters")) {
			cl_t cl;
			u_int32_t sz, len;

			for (cl = dir->head, len = sz = 0;
			    (sz += boot->ClusterSize) < dir->size; len++)
				cl = fat_get_cl_next(fat, cl);
			clearchain(fat, fat_get_cl_next(fat, cl));
			ret = fat_set_cl_next(fat, cl, CLUST_EOF);
			return (FSFATMOD | ret);
		} else
			return FSERROR;
	}
	return FSOK;
}

static const u_char dot_name[11]    = ".          ";
static const u_char dotdot_name[11] = "..         ";

/*
 * Basic sanity check if the subdirectory have good '.' and '..' entries,
 * and they are directory entries.  Further sanity checks are performed
 * when we traverse into it.
 */
static int
check_subdirectory(struct fat_descriptor *fat, struct dosDirEntry *dir)
{
	u_char *buf, *cp;
	off_t off;
	cl_t cl;
	int retval = FSOK;
	int fd;
	struct bootblock *boot;

	boot = fat_get_boot(fat);
	fd = fat_get_fd(fat);

	cl = dir->head;
	if (dir->parent && !fat_is_valid_cl(fat, cl)) {
		return FSERROR;
	}

	if (!(boot->flags & FAT32) && !dir->parent) {
		off = boot->bpbResSectors + boot->bpbFATs *
			boot->FATsecs;
	} else {
		off = (cl - CLUST_FIRST) * boot->bpbSecPerClust + boot->FirstCluster;
	}

	/*
	 * We only need to check the first two entries of the directory,
	 * which is found in the first sector of the directory entry,
	 * so read in only the first sector.
	 */
	buf = malloc(boot->bpbBytesPerSec);
	if (buf == NULL) {
		perr("No space for directory buffer (%u)",
		    boot->bpbBytesPerSec);
		return FSFATAL;
	}

	off *= boot->bpbBytesPerSec;
	if (lseek(fd, off, SEEK_SET) != off ||
	    read(fd, buf, boot->bpbBytesPerSec) != (ssize_t)boot->bpbBytesPerSec) {
		perr("Unable to read directory");
		free(buf);
		return FSFATAL;
	}

	/*
	 * Both `.' and `..' must be present and be the first two entries
	 * and be ATTR_DIRECTORY of a valid subdirectory.
	 */
	cp = buf;
	if (memcmp(cp, dot_name, sizeof(dot_name)) != 0 ||
	    (cp[11] & ATTR_DIRECTORY) != ATTR_DIRECTORY) {
		pwarn("%s: Incorrect `.' for %s.\n", __func__, dir->name);
		retval |= FSERROR;
	}
	cp += 32;
	if (memcmp(cp, dotdot_name, sizeof(dotdot_name)) != 0 ||
	    (cp[11] & ATTR_DIRECTORY) != ATTR_DIRECTORY) {
		pwarn("%s: Incorrect `..' for %s. \n", __func__, dir->name);
		retval |= FSERROR;
	}

	free(buf);
	return retval;
}

/*
 * Read a directory and
 *   - resolve long name records
 *   - enter file and directory records into the parent's list
 *   - push directories onto the todo-stack
 */
static int
readDosDirSection(struct fat_descriptor *fat, struct dosDirEntry *dir)
{
	struct bootblock *boot;
	struct dosDirEntry dirent, *d;
	u_char *p, *vallfn, *invlfn, *empty;
	off_t off;
	int fd, i, j, k, iosize, entries;
	bool is_legacyroot;
	cl_t cl, valcl = ~0, invcl = ~0, empcl = ~0;
	char *t;
	u_int lidx = 0;
	int shortSum;
	int mod = FSOK;
	size_t dirclusters;
#define	THISMOD	0x8000			/* Only used within this routine */

	boot = fat_get_boot(fat);
	fd = fat_get_fd(fat);

	cl = dir->head;
	if (dir->parent && (!fat_is_valid_cl(fat, cl))) {
		/*
		 * Already handled somewhere else.
		 */
		return FSOK;
	}
	shortSum = -1;
	vallfn = invlfn = empty = NULL;

	/*
	 * If we are checking the legacy root (for FAT12/FAT16),
	 * we will operate on the whole directory; otherwise, we
	 * will operate on one cluster at a time, and also take
	 * this opportunity to examine the chain.
	 *
	 * Derive how many entries we are going to encounter from
	 * the I/O size.
	 */
	is_legacyroot = (dir->parent == NULL && !(boot->flags & FAT32));
	if (is_legacyroot) {
		iosize = boot->bpbRootDirEnts * 32;
		entries = boot->bpbRootDirEnts;
	} else {
		iosize = boot->bpbSecPerClust * boot->bpbBytesPerSec;
		entries = iosize / 32;
		mod |= checkchain(fat, dir->head, &dirclusters);
	}

	do {
		if (is_legacyroot) {
			/*
			 * Special case for FAT12/FAT16 root -- read
			 * in the whole root directory.
			 */
			off = boot->bpbResSectors + boot->bpbFATs *
			    boot->FATsecs;
		} else {
			/*
			 * Otherwise, read in a cluster of the
			 * directory.
			 */
			off = (cl - CLUST_FIRST) * boot->bpbSecPerClust + boot->FirstCluster;
		}

		off *= boot->bpbBytesPerSec;
		if (lseek(fd, off, SEEK_SET) != off ||
		    read(fd, buffer, iosize) != iosize) {
			perr("Unable to read directory");
			return FSFATAL;
		}

		for (p = buffer, i = 0; i < entries; i++, p += 32) {
			if (dir->fsckflags & DIREMPWARN) {
				*p = SLOT_EMPTY;
				continue;
			}

			if (*p == SLOT_EMPTY || *p == SLOT_DELETED) {
				if (*p == SLOT_EMPTY) {
					dir->fsckflags |= DIREMPTY;
					empty = p;
					empcl = cl;
				}
				continue;
			}

			if (dir->fsckflags & DIREMPTY) {
				if (!(dir->fsckflags & DIREMPWARN)) {
					pwarn("%s has entries after end of directory\n",
					      fullpath(dir));
					if (ask(1, "Extend")) {
						u_char *q;

						dir->fsckflags &= ~DIREMPTY;
						if (delete(fat,
							   empcl, empty - buffer,
							   cl, p - buffer, 1) == FSFATAL)
							return FSFATAL;
						q = ((empcl == cl) ? empty : buffer);
						assert(q != NULL);
						for (; q < p; q += 32)
							*q = SLOT_DELETED;
						mod |= THISMOD|FSDIRMOD;
					} else if (ask(0, "Truncate"))
						dir->fsckflags |= DIREMPWARN;
				}
				if (dir->fsckflags & DIREMPWARN) {
					*p = SLOT_DELETED;
					mod |= THISMOD|FSDIRMOD;
					continue;
				} else if (dir->fsckflags & DIREMPTY)
					mod |= FSERROR;
				empty = NULL;
			}

			if (p[11] == ATTR_WIN95) {
				if (*p & LRFIRST) {
					if (shortSum != -1) {
						if (!invlfn) {
							invlfn = vallfn;
							invcl = valcl;
						}
					}
					memset(longName, 0, sizeof longName);
					shortSum = p[13];
					vallfn = p;
					valcl = cl;
				} else if (shortSum != p[13]
					   || lidx != (*p & LRNOMASK)) {
					if (!invlfn) {
						invlfn = vallfn;
						invcl = valcl;
					}
					if (!invlfn) {
						invlfn = p;
						invcl = cl;
					}
					vallfn = NULL;
				}
				lidx = *p & LRNOMASK;
				if (lidx == 0) {
					pwarn("invalid long name\n");
					if (!invlfn) {
						invlfn = vallfn;
						invcl = valcl;
					}
					vallfn = NULL;
					continue;
				}
				t = longName + --lidx * 13;
				for (k = 1; k < 11 && t < longName +
				    sizeof(longName); k += 2) {
					if (!p[k] && !p[k + 1])
						break;
					*t++ = p[k];
					/*
					 * Warn about those unusable chars in msdosfs here?	XXX
					 */
					if (p[k + 1])
						t[-1] = '?';
				}
				if (k >= 11)
					for (k = 14; k < 26 && t < longName + sizeof(longName); k += 2) {
						if (!p[k] && !p[k + 1])
							break;
						*t++ = p[k];
						if (p[k + 1])
							t[-1] = '?';
					}
				if (k >= 26)
					for (k = 28; k < 32 && t < longName + sizeof(longName); k += 2) {
						if (!p[k] && !p[k + 1])
							break;
						*t++ = p[k];
						if (p[k + 1])
							t[-1] = '?';
					}
				if (t >= longName + sizeof(longName)) {
					pwarn("long filename too long\n");
					if (!invlfn) {
						invlfn = vallfn;
						invcl = valcl;
					}
					vallfn = NULL;
				}
				if (p[26] | (p[27] << 8)) {
					pwarn("long filename record cluster start != 0\n");
					if (!invlfn) {
						invlfn = vallfn;
						invcl = cl;
					}
					vallfn = NULL;
				}
				continue;	/* long records don't carry further
						 * information */
			}

			/*
			 * This is a standard msdosfs directory entry.
			 */
			memset(&dirent, 0, sizeof dirent);

			/*
			 * it's a short name record, but we need to know
			 * more, so get the flags first.
			 */
			dirent.flags = p[11];

			/*
			 * Translate from 850 to ISO here		XXX
			 */
			for (j = 0; j < 8; j++)
				dirent.name[j] = p[j];
			dirent.name[8] = '\0';
			for (k = 7; k >= 0 && dirent.name[k] == ' '; k--)
				dirent.name[k] = '\0';
			if (k < 0 || dirent.name[k] != '\0')
				k++;
			if (dirent.name[0] == SLOT_E5)
				dirent.name[0] = 0xe5;

			if (dirent.flags & ATTR_VOLUME) {
				if (vallfn || invlfn) {
					mod |= removede(fat,
							invlfn ? invlfn : vallfn, p,
							invlfn ? invcl : valcl, -1, 0,
							fullpath(dir), 2);
					vallfn = NULL;
					invlfn = NULL;
				}
				continue;
			}

			if (p[8] != ' ')
				dirent.name[k++] = '.';
			for (j = 0; j < 3; j++)
				dirent.name[k++] = p[j+8];
			dirent.name[k] = '\0';
			for (k--; k >= 0 && dirent.name[k] == ' '; k--)
				dirent.name[k] = '\0';

			if (vallfn && shortSum != calcShortSum(p)) {
				if (!invlfn) {
					invlfn = vallfn;
					invcl = valcl;
				}
				vallfn = NULL;
			}
			dirent.head = p[26] | (p[27] << 8);
			if (boot->ClustMask == CLUST32_MASK)
				dirent.head |= (p[20] << 16) | (p[21] << 24);
			dirent.size = p[28] | (p[29] << 8) | (p[30] << 16) | (p[31] << 24);
			if (vallfn) {
				strlcpy(dirent.lname, longName,
				    sizeof(dirent.lname));
				longName[0] = '\0';
				shortSum = -1;
			}

			dirent.parent = dir;
			dirent.next = dir->child;

			if (invlfn) {
				mod |= k = removede(fat,
						    invlfn, vallfn ? vallfn : p,
						    invcl, vallfn ? valcl : cl, cl,
						    fullpath(&dirent), 0);
				if (mod & FSFATAL)
					return FSFATAL;
				if (vallfn
				    ? (valcl == cl && vallfn != buffer)
				    : p != buffer)
					if (k & FSDIRMOD)
						mod |= THISMOD;
			}

			vallfn = NULL; /* not used any longer */
			invlfn = NULL;

			/*
			 * Check if the directory entry is sane.
			 *
			 * '.' and '..' are skipped, their sanity is
			 * checked somewhere else.
			 *
			 * For everything else, check if we have a new,
			 * valid cluster chain (beginning of a file or
			 * directory that was never previously claimed
			 * by another file) when it's a non-empty file
			 * or a directory. The sanity of the cluster
			 * chain is checked at a later time when we
			 * traverse into the directory, or examine the
			 * file's directory entry.
			 *
			 * The only possible fix is to delete the entry
			 * if it's a directory; for file, we have to
			 * truncate the size to 0.
			 */
			if (!(dirent.flags & ATTR_DIRECTORY) ||
			    (strcmp(dirent.name, ".") != 0 &&
			    strcmp(dirent.name, "..") != 0)) {
				if ((dirent.size != 0 || (dirent.flags & ATTR_DIRECTORY)) &&
				    ((!fat_is_valid_cl(fat, dirent.head) ||
				    !fat_is_cl_head(fat, dirent.head)))) {
					if (!fat_is_valid_cl(fat, dirent.head)) {
						pwarn("%s starts with cluster out of range(%u)\n",
						    fullpath(&dirent),
						    dirent.head);
					} else {
						pwarn("%s doesn't start a new cluster chain\n",
						    fullpath(&dirent));
					}

					if (dirent.flags & ATTR_DIRECTORY) {
						if (ask(0, "Remove")) {
							*p = SLOT_DELETED;
							mod |= THISMOD|FSDIRMOD;
						} else
							mod |= FSERROR;
						continue;
					} else {
						if (ask(1, "Truncate")) {
							p[28] = p[29] = p[30] = p[31] = 0;
							p[26] = p[27] = 0;
							if (boot->ClustMask == CLUST32_MASK)
								p[20] = p[21] = 0;
							dirent.size = 0;
							dirent.head = 0;
							mod |= THISMOD|FSDIRMOD;
						} else
							mod |= FSERROR;
					}
				}
			}
			if (dirent.flags & ATTR_DIRECTORY) {
				/*
				 * gather more info for directories
				 */
				struct dirTodoNode *n;

				if (dirent.size) {
					pwarn("Directory %s has size != 0\n",
					      fullpath(&dirent));
					if (ask(1, "Correct")) {
						p[28] = p[29] = p[30] = p[31] = 0;
						dirent.size = 0;
						mod |= THISMOD|FSDIRMOD;
					} else
						mod |= FSERROR;
				}
				/*
				 * handle `.' and `..' specially
				 */
				if (strcmp(dirent.name, ".") == 0) {
					if (dirent.head != dir->head) {
						pwarn("`.' entry in %s has incorrect start cluster\n",
						      fullpath(dir));
						if (ask(1, "Correct")) {
							dirent.head = dir->head;
							p[26] = (u_char)dirent.head;
							p[27] = (u_char)(dirent.head >> 8);
							if (boot->ClustMask == CLUST32_MASK) {
								p[20] = (u_char)(dirent.head >> 16);
								p[21] = (u_char)(dirent.head >> 24);
							}
							mod |= THISMOD|FSDIRMOD;
						} else
							mod |= FSERROR;
					}
					continue;
				} else if (strcmp(dirent.name, "..") == 0) {
					if (dir->parent) {		/* XXX */
						if (!dir->parent->parent) {
							if (dirent.head) {
								pwarn("`..' entry in %s has non-zero start cluster\n",
								      fullpath(dir));
								if (ask(1, "Correct")) {
									dirent.head = 0;
									p[26] = p[27] = 0;
									if (boot->ClustMask == CLUST32_MASK)
										p[20] = p[21] = 0;
									mod |= THISMOD|FSDIRMOD;
								} else
									mod |= FSERROR;
							}
						} else if (dirent.head != dir->parent->head) {
							pwarn("`..' entry in %s has incorrect start cluster\n",
							      fullpath(dir));
							if (ask(1, "Correct")) {
								dirent.head = dir->parent->head;
								p[26] = (u_char)dirent.head;
								p[27] = (u_char)(dirent.head >> 8);
								if (boot->ClustMask == CLUST32_MASK) {
									p[20] = (u_char)(dirent.head >> 16);
									p[21] = (u_char)(dirent.head >> 24);
								}
								mod |= THISMOD|FSDIRMOD;
							} else
								mod |= FSERROR;
						}
					}
					continue;
				} else {
					/*
					 * Only one directory entry can point
					 * to dir->head, it's '.'.
					 */
					if (dirent.head == dir->head) {
						pwarn("%s entry in %s has incorrect start cluster\n",
								dirent.name, fullpath(dir));
						if (ask(1, "Remove")) {
							*p = SLOT_DELETED;
							mod |= THISMOD|FSDIRMOD;
						} else
							mod |= FSERROR;
						continue;
					} else if ((check_subdirectory(fat,
					    &dirent) & FSERROR) == FSERROR) {
						/*
						 * A subdirectory should have
						 * a dot (.) entry and a dot-dot
						 * (..) entry of ATTR_DIRECTORY,
						 * we will inspect further when
						 * traversing into it.
						 */
						if (ask(1, "Remove")) {
							*p = SLOT_DELETED;
							mod |= THISMOD|FSDIRMOD;
						} else
							mod |= FSERROR;
						continue;
					}
				}

				/* create directory tree node */
				if (!(d = newDosDirEntry())) {
					perr("No space for directory");
					return FSFATAL;
				}
				memcpy(d, &dirent, sizeof(struct dosDirEntry));
				/* link it into the tree */
				dir->child = d;

				/* Enter this directory into the todo list */
				if (!(n = newDirTodo())) {
					perr("No space for todo list");
					return FSFATAL;
				}
				n->next = pendingDirectories;
				n->dir = d;
				pendingDirectories = n;
			} else {
				mod |= k = checksize(fat, p, &dirent);
				if (k & FSDIRMOD)
					mod |= THISMOD;
			}
			boot->NumFiles++;
		}

		if (is_legacyroot) {
			/*
			 * Don't bother to write back right now because
			 * we may continue to make modification to the
			 * non-FAT32 root directory below.
			 */
			break;
		} else if (mod & THISMOD) {
			if (lseek(fd, off, SEEK_SET) != off
			    || write(fd, buffer, iosize) != iosize) {
				perr("Unable to write directory");
				return FSFATAL;
			}
			mod &= ~THISMOD;
		}
	} while (fat_is_valid_cl(fat, (cl = fat_get_cl_next(fat, cl))));
	if (invlfn || vallfn)
		mod |= removede(fat,
				invlfn ? invlfn : vallfn, p,
				invlfn ? invcl : valcl, -1, 0,
				fullpath(dir), 1);

	/*
	 * The root directory of non-FAT32 filesystems is in a special
	 * area and may have been modified above removede() without
	 * being written out.
	 */
	if ((mod & FSDIRMOD) && is_legacyroot) {
		if (lseek(fd, off, SEEK_SET) != off
		    || write(fd, buffer, iosize) != iosize) {
			perr("Unable to write directory");
			return FSFATAL;
		}
		mod &= ~THISMOD;
	}
	return mod & ~THISMOD;
}

int
handleDirTree(struct fat_descriptor *fat)
{
	int mod;

	mod = readDosDirSection(fat, rootDir);
	if (mod & FSFATAL)
		return FSFATAL;

	/*
	 * process the directory todo list
	 */
	while (pendingDirectories) {
		struct dosDirEntry *dir = pendingDirectories->dir;
		struct dirTodoNode *n = pendingDirectories->next;

		/*
		 * remove TODO entry now, the list might change during
		 * directory reads
		 */
		freeDirTodo(pendingDirectories);
		pendingDirectories = n;

		/*
		 * handle subdirectory
		 */
		mod |= readDosDirSection(fat, dir);
		if (mod & FSFATAL)
			return FSFATAL;
	}

	return mod;
}

/*
 * Try to reconnect a FAT chain into dir
 */
static u_char *lfbuf;
static cl_t lfcl;
static off_t lfoff;

int
reconnect(struct fat_descriptor *fat, cl_t head, size_t length)
{
	struct bootblock *boot = fat_get_boot(fat);
	struct dosDirEntry d;
	int len, dosfs;
	u_char *p;

	dosfs = fat_get_fd(fat);

	if (!ask(1, "Reconnect"))
		return FSERROR;

	if (!lostDir) {
		for (lostDir = rootDir->child; lostDir; lostDir = lostDir->next) {
			if (!strcmp(lostDir->name, LOSTDIR))
				break;
		}
		if (!lostDir) {		/* Create LOSTDIR?		XXX */
			pwarn("No %s directory\n", LOSTDIR);
			return FSERROR;
		}
	}
	if (!lfbuf) {
		lfbuf = malloc(boot->ClusterSize);
		if (!lfbuf) {
			perr("No space for buffer");
			return FSFATAL;
		}
		p = NULL;
	} else
		p = lfbuf;
	while (1) {
		if (p)
			for (; p < lfbuf + boot->ClusterSize; p += 32)
				if (*p == SLOT_EMPTY
				    || *p == SLOT_DELETED)
					break;
		if (p && p < lfbuf + boot->ClusterSize)
			break;
		lfcl = p ? fat_get_cl_next(fat, lfcl) : lostDir->head;
		if (lfcl < CLUST_FIRST || lfcl >= boot->NumClusters) {
			/* Extend LOSTDIR?				XXX */
			pwarn("No space in %s\n", LOSTDIR);
			lfcl = (lostDir->head < boot->NumClusters) ? lostDir->head : 0;
			return FSERROR;
		}
		lfoff = (lfcl - CLUST_FIRST) * boot->ClusterSize
		    + boot->FirstCluster * boot->bpbBytesPerSec;

		if (lseek(dosfs, lfoff, SEEK_SET) != lfoff
		    || (size_t)read(dosfs, lfbuf, boot->ClusterSize) != boot->ClusterSize) {
			perr("could not read LOST.DIR");
			return FSFATAL;
		}
		p = lfbuf;
	}

	boot->NumFiles++;
	/* Ensure uniqueness of entry here!				XXX */
	memset(&d, 0, sizeof d);
	/* worst case -1 = 4294967295, 10 digits */
	len = snprintf(d.name, sizeof(d.name), "%u", head);
	d.flags = 0;
	d.head = head;
	d.size = length * boot->ClusterSize;

	memcpy(p, d.name, len);
	memset(p + len, ' ', 11 - len);
	memset(p + 11, 0, 32 - 11);
	p[26] = (u_char)d.head;
	p[27] = (u_char)(d.head >> 8);
	if (boot->ClustMask == CLUST32_MASK) {
		p[20] = (u_char)(d.head >> 16);
		p[21] = (u_char)(d.head >> 24);
	}
	p[28] = (u_char)d.size;
	p[29] = (u_char)(d.size >> 8);
	p[30] = (u_char)(d.size >> 16);
	p[31] = (u_char)(d.size >> 24);
	if (lseek(dosfs, lfoff, SEEK_SET) != lfoff
	    || (size_t)write(dosfs, lfbuf, boot->ClusterSize) != boot->ClusterSize) {
		perr("could not write LOST.DIR");
		return FSFATAL;
	}
	return FSDIRMOD;
}

void
finishlf(void)
{
	if (lfbuf)
		free(lfbuf);
	lfbuf = NULL;
}