Btrfs: prevent loops in the directory tree when creating snapshots

[linux-2.6] / fs / ntfs / namei.c

/*
 * namei.c - NTFS kernel directory inode operations. Part of the Linux-NTFS
 *           project.
 *
 * Copyright (c) 2001-2006 Anton Altaparmakov
 *
 * This program/include file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program/include file is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/dcache.h>
#include <linux/exportfs.h>
#include <linux/security.h>

#include "attrib.h"
#include "debug.h"
#include "dir.h"
#include "mft.h"
#include "ntfs.h"

/**
 * ntfs_lookup - find the inode represented by a dentry in a directory inode
 * @dir_ino:    directory inode in which to look for the inode
 * @dent:       dentry representing the inode to look for
 * @nd:         lookup nameidata
 *
 * In short, ntfs_lookup() looks for the inode represented by the dentry @dent
 * in the directory inode @dir_ino and if found attaches the inode to the
 * dentry @dent.
 *
 * In more detail, the dentry @dent specifies which inode to look for by
 * supplying the name of the inode in @dent->d_name.name. ntfs_lookup()
 * converts the name to Unicode and walks the contents of the directory inode
 * @dir_ino looking for the converted Unicode name. If the name is found in the
 * directory, the corresponding inode is loaded by calling ntfs_iget() on its
 * inode number and the inode is associated with the dentry @dent via a call to
 * d_splice_alias().
 *
 * If the name is not found in the directory, a NULL inode is inserted into the
 * dentry @dent via a call to d_add(). The dentry is then termed a negative
 * dentry.
 *
 * Only if an actual error occurs, do we return an error via ERR_PTR().
 *
 * In order to handle the case insensitivity issues of NTFS with regards to the
 * dcache and the dcache requiring only one dentry per directory, we deal with
 * dentry aliases that only differ in case in ->ntfs_lookup() while maintaining
 * a case sensitive dcache. This means that we get the full benefit of dcache
 * speed when the file/directory is looked up with the same case as returned by
 * ->ntfs_readdir() but that a lookup for any other case (or for the short file
 * name) will not find anything in dcache and will enter ->ntfs_lookup()
 * instead, where we search the directory for a fully matching file name
 * (including case) and if that is not found, we search for a file name that
 * matches with different case and if that has non-POSIX semantics we return
 * that. We actually do only one search (case sensitive) and keep tabs on
 * whether we have found a case insensitive match in the process.
 *
 * To simplify matters for us, we do not treat the short vs long filenames as
 * two hard links but instead if the lookup matches a short filename, we
 * return the dentry for the corresponding long filename instead.
 *
 * There are three cases we need to distinguish here:
 *
 * 1) @dent perfectly matches (i.e. including case) a directory entry with a
 *    file name in the WIN32 or POSIX namespaces. In this case
 *    ntfs_lookup_inode_by_name() will return with name set to NULL and we
 *    just d_splice_alias() @dent.
 * 2) @dent matches (not including case) a directory entry with a file name in
 *    the WIN32 namespace. In this case ntfs_lookup_inode_by_name() will return
 *    with name set to point to a kmalloc()ed ntfs_name structure containing
 *    the properly cased little endian Unicode name. We convert the name to the
 *    current NLS code page, search if a dentry with this name already exists
 *    and if so return that instead of @dent.  At this point things are
 *    complicated by the possibility of 'disconnected' dentries due to NFS
 *    which we deal with appropriately (see the code comments).  The VFS will
 *    then destroy the old @dent and use the one we returned.  If a dentry is
 *    not found, we allocate a new one, d_splice_alias() it, and return it as
 *    above.
 * 3) @dent matches either perfectly or not (i.e. we don't care about case) a
 *    directory entry with a file name in the DOS namespace. In this case
 *    ntfs_lookup_inode_by_name() will return with name set to point to a
 *    kmalloc()ed ntfs_name structure containing the mft reference (cpu endian)
 *    of the inode. We use the mft reference to read the inode and to find the
 *    file name in the WIN32 namespace corresponding to the matched short file
 *    name. We then convert the name to the current NLS code page, and proceed
 *    searching for a dentry with this name, etc, as in case 2), above.
 *
 * Locking: Caller must hold i_mutex on the directory.
 */
static struct dentry *ntfs_lookup(struct inode *dir_ino, struct dentry *dent,
                struct nameidata *nd)
{
        ntfs_volume *vol = NTFS_SB(dir_ino->i_sb);
        struct inode *dent_inode;
        ntfschar *uname;
        ntfs_name *name = NULL;
        MFT_REF mref;
        unsigned long dent_ino;
        int uname_len;

        ntfs_debug("Looking up %s in directory inode 0x%lx.",
                        dent->d_name.name, dir_ino->i_ino);
        /* Convert the name of the dentry to Unicode. */
        uname_len = ntfs_nlstoucs(vol, dent->d_name.name, dent->d_name.len,
                        &uname);
        if (uname_len < 0) {
                if (uname_len != -ENAMETOOLONG)
                        ntfs_error(vol->sb, "Failed to convert name to "
                                        "Unicode.");
                return ERR_PTR(uname_len);
        }
        mref = ntfs_lookup_inode_by_name(NTFS_I(dir_ino), uname, uname_len,
                        &name);
        kmem_cache_free(ntfs_name_cache, uname);
        if (!IS_ERR_MREF(mref)) {
                dent_ino = MREF(mref);
                ntfs_debug("Found inode 0x%lx. Calling ntfs_iget.", dent_ino);
                dent_inode = ntfs_iget(vol->sb, dent_ino);
                if (likely(!IS_ERR(dent_inode))) {
                        /* Consistency check. */
                        if (is_bad_inode(dent_inode) || MSEQNO(mref) ==
                                        NTFS_I(dent_inode)->seq_no ||
                                        dent_ino == FILE_MFT) {
                                /* Perfect WIN32/POSIX match. -- Case 1. */
                                if (!name) {
                                        ntfs_debug("Done.  (Case 1.)");
                                        return d_splice_alias(dent_inode, dent);
                                }
                                /*
                                 * We are too indented.  Handle imperfect
                                 * matches and short file names further below.
                                 */
                                goto handle_name;
                        }
                        ntfs_error(vol->sb, "Found stale reference to inode "
                                        "0x%lx (reference sequence number = "
                                        "0x%x, inode sequence number = 0x%x), "
                                        "returning -EIO. Run chkdsk.",
                                        dent_ino, MSEQNO(mref),
                                        NTFS_I(dent_inode)->seq_no);
                        iput(dent_inode);
                        dent_inode = ERR_PTR(-EIO);
                } else
                        ntfs_error(vol->sb, "ntfs_iget(0x%lx) failed with "
                                        "error code %li.", dent_ino,
                                        PTR_ERR(dent_inode));
                kfree(name);
                /* Return the error code. */
                return (struct dentry *)dent_inode;
        }
        /* It is guaranteed that @name is no longer allocated at this point. */
        if (MREF_ERR(mref) == -ENOENT) {
                ntfs_debug("Entry was not found, adding negative dentry.");
                /* The dcache will handle negative entries. */
                d_add(dent, NULL);
                ntfs_debug("Done.");
                return NULL;
        }
        ntfs_error(vol->sb, "ntfs_lookup_ino_by_name() failed with error "
                        "code %i.", -MREF_ERR(mref));
        return ERR_PTR(MREF_ERR(mref));
        // TODO: Consider moving this lot to a separate function! (AIA)
handle_name:
   {
        MFT_RECORD *m;
        ntfs_attr_search_ctx *ctx;
        ntfs_inode *ni = NTFS_I(dent_inode);
        int err;
        struct qstr nls_name;

        nls_name.name = NULL;
        if (name->type != FILE_NAME_DOS) {                      /* Case 2. */
                ntfs_debug("Case 2.");
                nls_name.len = (unsigned)ntfs_ucstonls(vol,
                                (ntfschar*)&name->name, name->len,
                                (unsigned char**)&nls_name.name, 0);
                kfree(name);
        } else /* if (name->type == FILE_NAME_DOS) */ {         /* Case 3. */
                FILE_NAME_ATTR *fn;

                ntfs_debug("Case 3.");
                kfree(name);

                /* Find the WIN32 name corresponding to the matched DOS name. */
                ni = NTFS_I(dent_inode);
                m = map_mft_record(ni);
                if (IS_ERR(m)) {
                        err = PTR_ERR(m);
                        m = NULL;
                        ctx = NULL;
                        goto err_out;
                }
                ctx = ntfs_attr_get_search_ctx(ni, m);
                if (unlikely(!ctx)) {
                        err = -ENOMEM;
                        goto err_out;
                }
                do {
                        ATTR_RECORD *a;
                        u32 val_len;

                        err = ntfs_attr_lookup(AT_FILE_NAME, NULL, 0, 0, 0,
                                        NULL, 0, ctx);
                        if (unlikely(err)) {
                                ntfs_error(vol->sb, "Inode corrupt: No WIN32 "
                                                "namespace counterpart to DOS "
                                                "file name. Run chkdsk.");
                                if (err == -ENOENT)
                                        err = -EIO;
                                goto err_out;
                        }
                        /* Consistency checks. */
                        a = ctx->attr;
                        if (a->non_resident || a->flags)
                                goto eio_err_out;
                        val_len = le32_to_cpu(a->data.resident.value_length);
                        if (le16_to_cpu(a->data.resident.value_offset) +
                                        val_len > le32_to_cpu(a->length))
                                goto eio_err_out;
                        fn = (FILE_NAME_ATTR*)((u8*)ctx->attr + le16_to_cpu(
                                        ctx->attr->data.resident.value_offset));
                        if ((u32)(fn->file_name_length * sizeof(ntfschar) +
                                        sizeof(FILE_NAME_ATTR)) > val_len)
                                goto eio_err_out;
                } while (fn->file_name_type != FILE_NAME_WIN32);

                /* Convert the found WIN32 name to current NLS code page. */
                nls_name.len = (unsigned)ntfs_ucstonls(vol,
                                (ntfschar*)&fn->file_name, fn->file_name_length,
                                (unsigned char**)&nls_name.name, 0);

                ntfs_attr_put_search_ctx(ctx);
                unmap_mft_record(ni);
        }
        m = NULL;
        ctx = NULL;

        /* Check if a conversion error occurred. */
        if ((signed)nls_name.len < 0) {
                err = (signed)nls_name.len;
                goto err_out;
        }
        nls_name.hash = full_name_hash(nls_name.name, nls_name.len);

        dent = d_add_ci(dent, dent_inode, &nls_name);
        kfree(nls_name.name);
        return dent;

eio_err_out:
        ntfs_error(vol->sb, "Illegal file name attribute. Run chkdsk.");
        err = -EIO;
err_out:
        if (ctx)
                ntfs_attr_put_search_ctx(ctx);
        if (m)
                unmap_mft_record(ni);
        iput(dent_inode);
        ntfs_error(vol->sb, "Failed, returning error code %i.", err);
        return ERR_PTR(err);
   }
}

/**
 * Inode operations for directories.
 */
const struct inode_operations ntfs_dir_inode_ops = {
        .lookup = ntfs_lookup,  /* VFS: Lookup directory. */
};

/**
 * ntfs_get_parent - find the dentry of the parent of a given directory dentry
 * @child_dent:         dentry of the directory whose parent directory to find
 *
 * Find the dentry for the parent directory of the directory specified by the
 * dentry @child_dent.  This function is called from
 * fs/exportfs/expfs.c::find_exported_dentry() which in turn is called from the
 * default ->decode_fh() which is export_decode_fh() in the same file.
 *
 * The code is based on the ext3 ->get_parent() implementation found in
 * fs/ext3/namei.c::ext3_get_parent().
 *
 * Note: ntfs_get_parent() is called with @child_dent->d_inode->i_mutex down.
 *
 * Return the dentry of the parent directory on success or the error code on
 * error (IS_ERR() is true).
 */
static struct dentry *ntfs_get_parent(struct dentry *child_dent)
{
        struct inode *vi = child_dent->d_inode;
        ntfs_inode *ni = NTFS_I(vi);
        MFT_RECORD *mrec;
        ntfs_attr_search_ctx *ctx;
        ATTR_RECORD *attr;
        FILE_NAME_ATTR *fn;
        struct inode *parent_vi;
        struct dentry *parent_dent;
        unsigned long parent_ino;
        int err;

        ntfs_debug("Entering for inode 0x%lx.", vi->i_ino);
        /* Get the mft record of the inode belonging to the child dentry. */
        mrec = map_mft_record(ni);
        if (IS_ERR(mrec))
                return (struct dentry *)mrec;
        /* Find the first file name attribute in the mft record. */
        ctx = ntfs_attr_get_search_ctx(ni, mrec);
        if (unlikely(!ctx)) {
                unmap_mft_record(ni);
                return ERR_PTR(-ENOMEM);
        }
try_next:
        err = ntfs_attr_lookup(AT_FILE_NAME, NULL, 0, CASE_SENSITIVE, 0, NULL,
                        0, ctx);
        if (unlikely(err)) {
                ntfs_attr_put_search_ctx(ctx);
                unmap_mft_record(ni);
                if (err == -ENOENT)
                        ntfs_error(vi->i_sb, "Inode 0x%lx does not have a "
                                        "file name attribute.  Run chkdsk.",
                                        vi->i_ino);
                return ERR_PTR(err);
        }
        attr = ctx->attr;
        if (unlikely(attr->non_resident))
                goto try_next;
        fn = (FILE_NAME_ATTR *)((u8 *)attr +
                        le16_to_cpu(attr->data.resident.value_offset));
        if (unlikely((u8 *)fn + le32_to_cpu(attr->data.resident.value_length) >
                        (u8*)attr + le32_to_cpu(attr->length)))
                goto try_next;
        /* Get the inode number of the parent directory. */
        parent_ino = MREF_LE(fn->parent_directory);
        /* Release the search context and the mft record of the child. */
        ntfs_attr_put_search_ctx(ctx);
        unmap_mft_record(ni);
        /* Get the inode of the parent directory. */
        parent_vi = ntfs_iget(vi->i_sb, parent_ino);
        if (IS_ERR(parent_vi) || unlikely(is_bad_inode(parent_vi))) {
                if (!IS_ERR(parent_vi))
                        iput(parent_vi);
                ntfs_error(vi->i_sb, "Failed to get parent directory inode "
                                "0x%lx of child inode 0x%lx.", parent_ino,
                                vi->i_ino);
                return ERR_PTR(-EACCES);
        }
        /* Finally get a dentry for the parent directory and return it. */
        parent_dent = d_alloc_anon(parent_vi);
        if (unlikely(!parent_dent)) {
                iput(parent_vi);
                return ERR_PTR(-ENOMEM);
        }
        ntfs_debug("Done for inode 0x%lx.", vi->i_ino);
        return parent_dent;
}

static struct inode *ntfs_nfs_get_inode(struct super_block *sb,
                u64 ino, u32 generation)
{
        struct inode *inode;

        inode = ntfs_iget(sb, ino);
        if (!IS_ERR(inode)) {
                if (is_bad_inode(inode) || inode->i_generation != generation) {
                        iput(inode);
                        inode = ERR_PTR(-ESTALE);
                }
        }

        return inode;
}

static struct dentry *ntfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
                int fh_len, int fh_type)
{
        return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
                                    ntfs_nfs_get_inode);
}

static struct dentry *ntfs_fh_to_parent(struct super_block *sb, struct fid *fid,
                int fh_len, int fh_type)
{
        return generic_fh_to_parent(sb, fid, fh_len, fh_type,
                                    ntfs_nfs_get_inode);
}

/**
 * Export operations allowing NFS exporting of mounted NTFS partitions.
 *
 * We use the default ->encode_fh() for now.  Note that they
 * use 32 bits to store the inode number which is an unsigned long so on 64-bit
 * architectures is usually 64 bits so it would all fail horribly on huge
 * volumes.  I guess we need to define our own encode and decode fh functions
 * that store 64-bit inode numbers at some point but for now we will ignore the
 * problem...
 *
 * We also use the default ->get_name() helper (used by ->decode_fh() via
 * fs/exportfs/expfs.c::find_exported_dentry()) as that is completely fs
 * independent.
 *
 * The default ->get_parent() just returns -EACCES so we have to provide our
 * own and the default ->get_dentry() is incompatible with NTFS due to not
 * allowing the inode number 0 which is used in NTFS for the system file $MFT
 * and due to using iget() whereas NTFS needs ntfs_iget().
 */
const struct export_operations ntfs_export_ops = {
        .get_parent     = ntfs_get_parent,      /* Find the parent of a given
                                                   directory. */
        .fh_to_dentry   = ntfs_fh_to_dentry,
        .fh_to_parent   = ntfs_fh_to_parent,
};