// SPDX-License-Identifier: GPL-2.0-or-later
/* AFS dynamic root handling
 *
 * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/dns_resolver.h>
#include "internal.h"

static atomic_t afs_autocell_ino;

/*
 * iget5() comparator for inode created by autocell operations
 *
 * These pseudo inodes don't match anything.
 */
static int afs_iget5_pseudo_test(struct inode *inode, void *opaque)
{
        return 0;
}

/*
 * iget5() inode initialiser
 */
static int afs_iget5_pseudo_set(struct inode *inode, void *opaque)
{
        struct afs_super_info *as = AFS_FS_S(inode->i_sb);
        struct afs_vnode *vnode = AFS_FS_I(inode);
        struct afs_fid *fid = opaque;

        vnode->volume           = as->volume;
        vnode->fid              = *fid;
        inode->i_ino            = fid->vnode;
        inode->i_generation     = fid->unique;
        return 0;
}

/*
 * Create an inode for a dynamic root directory or an autocell dynamic
 * automount dir.
 */
struct inode *afs_iget_pseudo_dir(struct super_block *sb, bool root)
{
        struct afs_super_info *as = AFS_FS_S(sb);
        struct afs_vnode *vnode;
        struct inode *inode;
        struct afs_fid fid = {};

        _enter("");

        if (as->volume)
                fid.vid = as->volume->vid;
        if (root) {
                fid.vnode = 1;
                fid.unique = 1;
        } else {
                fid.vnode = atomic_inc_return(&afs_autocell_ino);
                fid.unique = 0;
        }

        inode = iget5_locked(sb, fid.vnode,
                             afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
        if (!inode) {
                _leave(" = -ENOMEM");
                return ERR_PTR(-ENOMEM);
        }

        _debug("GOT INODE %p { ino=%lu, vl=%llx, vn=%llx, u=%x }",
               inode, inode->i_ino, fid.vid, fid.vnode, fid.unique);

        vnode = AFS_FS_I(inode);

        /* there shouldn't be an existing inode */
        BUG_ON(!(inode->i_state & I_NEW));

        inode->i_size           = 0;
        inode->i_mode           = S_IFDIR | S_IRUGO | S_IXUGO;
        if (root) {
                inode->i_op     = &afs_dynroot_inode_operations;
                inode->i_fop    = &simple_dir_operations;
        } else {
                inode->i_op     = &afs_autocell_inode_operations;
        }
        set_nlink(inode, 2);
        inode->i_uid            = GLOBAL_ROOT_UID;
        inode->i_gid            = GLOBAL_ROOT_GID;
        inode->i_ctime = inode->i_atime = inode->i_mtime = current_time(inode);
        inode->i_blocks         = 0;
        inode->i_generation     = 0;

        set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
        if (!root) {
                set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
                inode->i_flags |= S_AUTOMOUNT;
        }

        inode->i_flags |= S_NOATIME;
        unlock_new_inode(inode);
        _leave(" = %p", inode);
        return inode;
}

/*
 * Probe to see if a cell may exist.  This prevents positive dentries from
 * being created unnecessarily.
 */
static int afs_probe_cell_name(struct dentry *dentry)
{
        struct afs_cell *cell;
        struct afs_net *net = afs_d2net(dentry);
        const char *name = dentry->d_name.name;
        size_t len = dentry->d_name.len;
        int ret;

        /* Names prefixed with a dot are R/W mounts. */
        if (name[0] == '.') {
                if (len == 1)
                        return -EINVAL;
                name++;
                len--;
        }

        cell = afs_lookup_cell_rcu(net, name, len);
        if (!IS_ERR(cell)) {
                afs_put_cell(net, cell);
                return 0;
        }

        ret = dns_query(net->net, "afsdb", name, len, "srv=1",
                        NULL, NULL, false);
        if (ret == -ENODATA)
                ret = -EDESTADDRREQ;
        return ret;
}

/*
 * Try to auto mount the mountpoint with pseudo directory, if the autocell
 * operation is setted.
 */
struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
{
        struct afs_vnode *vnode = AFS_FS_I(dir);
        struct inode *inode;
        int ret = -ENOENT;

        _enter("%p{%pd}, {%llx:%llu}",
               dentry, dentry, vnode->fid.vid, vnode->fid.vnode);

        if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
                goto out;

        ret = afs_probe_cell_name(dentry);
        if (ret < 0)
                goto out;

        inode = afs_iget_pseudo_dir(dir->i_sb, false);
        if (IS_ERR(inode)) {
                ret = PTR_ERR(inode);
                goto out;
        }

        _leave("= %p", inode);
        return inode;

out:
        _leave("= %d", ret);
        return ret == -ENOENT ? NULL : ERR_PTR(ret);
}

/*
 * Look up @cell in a dynroot directory.  This is a substitution for the
 * local cell name for the net namespace.
 */
static struct dentry *afs_lookup_atcell(struct dentry *dentry)
{
        struct afs_cell *cell;
        struct afs_net *net = afs_d2net(dentry);
        struct dentry *ret;
        unsigned int seq = 0;
        char *name;
        int len;

        if (!net->ws_cell)
                return ERR_PTR(-ENOENT);

        ret = ERR_PTR(-ENOMEM);
        name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
        if (!name)
                goto out_p;

        rcu_read_lock();
        do {
                read_seqbegin_or_lock(&net->cells_lock, &seq);
                cell = rcu_dereference_raw(net->ws_cell);
                if (cell) {
                        len = cell->name_len;
                        memcpy(name, cell->name, len + 1);
                }
        } while (need_seqretry(&net->cells_lock, seq));
        done_seqretry(&net->cells_lock, seq);
        rcu_read_unlock();

        ret = ERR_PTR(-ENOENT);
        if (!cell)
                goto out_n;

        ret = lookup_one_len(name, dentry->d_parent, len);

        /* We don't want to d_add() the @cell dentry here as we don't want to
         * the cached dentry to hide changes to the local cell name.
         */

out_n:
        kfree(name);
out_p:
        return ret;
}

/*
 * Look up an entry in a dynroot directory.
 */
static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
                                         unsigned int flags)
{
        _enter("%pd", dentry);

        ASSERTCMP(d_inode(dentry), ==, NULL);

        if (flags & LOOKUP_CREATE)
                return ERR_PTR(-EOPNOTSUPP);

        if (dentry->d_name.len >= AFSNAMEMAX) {
                _leave(" = -ENAMETOOLONG");
                return ERR_PTR(-ENAMETOOLONG);
        }

        if (dentry->d_name.len == 5 &&
            memcmp(dentry->d_name.name, "@cell", 5) == 0)
                return afs_lookup_atcell(dentry);

        return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
}

const struct inode_operations afs_dynroot_inode_operations = {
        .lookup         = afs_dynroot_lookup,
};

/*
 * Dirs in the dynamic root don't need revalidation.
 */
static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
{
        return 1;
}

/*
 * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
 * sleep)
 * - called from dput() when d_count is going to 0.
 * - return 1 to request dentry be unhashed, 0 otherwise
 */
static int afs_dynroot_d_delete(const struct dentry *dentry)
{
        return d_really_is_positive(dentry);
}

const struct dentry_operations afs_dynroot_dentry_operations = {
        .d_revalidate   = afs_dynroot_d_revalidate,
        .d_delete       = afs_dynroot_d_delete,
        .d_release      = afs_d_release,
        .d_automount    = afs_d_automount,
};

/*
 * Create a manually added cell mount directory.
 * - The caller must hold net->proc_cells_lock
 */
int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
{
        struct super_block *sb = net->dynroot_sb;
        struct dentry *root, *subdir;
        int ret;

        if (!sb || atomic_read(&sb->s_active) == 0)
                return 0;

        /* Let the ->lookup op do the creation */
        root = sb->s_root;
        inode_lock(root->d_inode);
        subdir = lookup_one_len(cell->name, root, cell->name_len);
        if (IS_ERR(subdir)) {
                ret = PTR_ERR(subdir);
                goto unlock;
        }

        /* Note that we're retaining an extra ref on the dentry */
        subdir->d_fsdata = (void *)1UL;
        ret = 0;
unlock:
        inode_unlock(root->d_inode);
        return ret;
}

/*
 * Remove a manually added cell mount directory.
 * - The caller must hold net->proc_cells_lock
 */
void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
{
        struct super_block *sb = net->dynroot_sb;
        struct dentry *root, *subdir;

        if (!sb || atomic_read(&sb->s_active) == 0)
                return;

        root = sb->s_root;
        inode_lock(root->d_inode);

        /* Don't want to trigger a lookup call, which will re-add the cell */
        subdir = try_lookup_one_len(cell->name, root, cell->name_len);
        if (IS_ERR_OR_NULL(subdir)) {
                _debug("lookup %ld", PTR_ERR(subdir));
                goto no_dentry;
        }

        _debug("rmdir %pd %u", subdir, d_count(subdir));

        if (subdir->d_fsdata) {
                _debug("unpin %u", d_count(subdir));
                subdir->d_fsdata = NULL;
                dput(subdir);
        }
        dput(subdir);
no_dentry:
        inode_unlock(root->d_inode);
        _leave("");
}

/*
 * Populate a newly created dynamic root with cell names.
 */
int afs_dynroot_populate(struct super_block *sb)
{
        struct afs_cell *cell;
        struct afs_net *net = afs_sb2net(sb);
        int ret;

        mutex_lock(&net->proc_cells_lock);

        net->dynroot_sb = sb;
        hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
                ret = afs_dynroot_mkdir(net, cell);
                if (ret < 0)
                        goto error;
        }

        ret = 0;
out:
        mutex_unlock(&net->proc_cells_lock);
        return ret;

error:
        net->dynroot_sb = NULL;
        goto out;
}

/*
 * When a dynamic root that's in the process of being destroyed, depopulate it
 * of pinned directories.
 */
void afs_dynroot_depopulate(struct super_block *sb)
{
        struct afs_net *net = afs_sb2net(sb);
        struct dentry *root = sb->s_root, *subdir, *tmp;

        /* Prevent more subdirs from being created */
        mutex_lock(&net->proc_cells_lock);
        if (net->dynroot_sb == sb)
                net->dynroot_sb = NULL;
        mutex_unlock(&net->proc_cells_lock);

        if (root) {
                inode_lock(root->d_inode);

                /* Remove all the pins for dirs created for manually added cells */
                list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
                        if (subdir->d_fsdata) {
                                subdir->d_fsdata = NULL;
                                dput(subdir);
                        }
                }

                inode_unlock(root->d_inode);
        }
}