1/* dir.c: AFS dynamic root handling
  2 *
  3 * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
  4 * Written by David Howells (dhowells@redhat.com)
  5 *
  6 * This program is free software; you can redistribute it and/or
  7 * modify it under the terms of the GNU General Public Licence
  8 * as published by the Free Software Foundation; either version
  9 * 2 of the Licence, or (at your option) any later version.
 10 */
 11
 12#include <linux/fs.h>
 13#include <linux/namei.h>
 14#include <linux/dns_resolver.h>
 15#include "internal.h"
 16
 17const struct file_operations afs_dynroot_file_operations = {
 18	.open		= dcache_dir_open,
 19	.release	= dcache_dir_close,
 20	.iterate_shared	= dcache_readdir,
 21	.llseek		= dcache_dir_lseek,
 22};
 23
 24/*
 25 * Probe to see if a cell may exist.  This prevents positive dentries from
 26 * being created unnecessarily.
 27 */
 28static int afs_probe_cell_name(struct dentry *dentry)
 29{
 30	struct afs_cell *cell;
 31	const char *name = dentry->d_name.name;
 32	size_t len = dentry->d_name.len;
 33	int ret;
 34
 35	/* Names prefixed with a dot are R/W mounts. */
 36	if (name[0] == '.') {
 37		if (len == 1)
 38			return -EINVAL;
 39		name++;
 40		len--;
 41	}
 42
 43	cell = afs_lookup_cell_rcu(afs_d2net(dentry), name, len);
 44	if (!IS_ERR(cell)) {
 45		afs_put_cell(afs_d2net(dentry), cell);
 46		return 0;
 47	}
 48
 49	ret = dns_query("afsdb", name, len, "ipv4", NULL, NULL);
 50	if (ret == -ENODATA)
 51		ret = -EDESTADDRREQ;
 52	return ret;
 53}
 54
 55/*
 56 * Try to auto mount the mountpoint with pseudo directory, if the autocell
 57 * operation is setted.
 58 */
 59struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
 60{
 61	struct afs_vnode *vnode = AFS_FS_I(dir);
 62	struct inode *inode;
 63	int ret = -ENOENT;
 64
 65	_enter("%p{%pd}, {%x:%u}",
 66	       dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
 67
 68	if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
 69		goto out;
 70
 71	ret = afs_probe_cell_name(dentry);
 72	if (ret < 0)
 73		goto out;
 74
 75	inode = afs_iget_pseudo_dir(dir->i_sb, false);
 76	if (IS_ERR(inode)) {
 77		ret = PTR_ERR(inode);
 78		goto out;
 79	}
 80
 81	_leave("= %p", inode);
 82	return inode;
 83
 84out:
 85	_leave("= %d", ret);
 86	return ERR_PTR(ret);
 87}
 88
 89/*
 90 * Look up @cell in a dynroot directory.  This is a substitution for the
 91 * local cell name for the net namespace.
 92 */
 93static struct dentry *afs_lookup_atcell(struct dentry *dentry)
 94{
 95	struct afs_cell *cell;
 96	struct afs_net *net = afs_d2net(dentry);
 97	struct dentry *ret;
 98	unsigned int seq = 0;
 99	char *name;
100	int len;
101
102	if (!net->ws_cell)
103		return ERR_PTR(-ENOENT);
104
105	ret = ERR_PTR(-ENOMEM);
106	name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
107	if (!name)
108		goto out_p;
109
110	rcu_read_lock();
111	do {
112		read_seqbegin_or_lock(&net->cells_lock, &seq);
113		cell = rcu_dereference_raw(net->ws_cell);
114		if (cell) {
115			len = cell->name_len;
116			memcpy(name, cell->name, len + 1);
117		}
118	} while (need_seqretry(&net->cells_lock, seq));
119	done_seqretry(&net->cells_lock, seq);
120	rcu_read_unlock();
121
122	ret = ERR_PTR(-ENOENT);
123	if (!cell)
124		goto out_n;
125
126	ret = lookup_one_len(name, dentry->d_parent, len);
127
128	/* We don't want to d_add() the @cell dentry here as we don't want to
129	 * the cached dentry to hide changes to the local cell name.
130	 */
131
132out_n:
133	kfree(name);
134out_p:
135	return ret;
136}
137
138/*
139 * Look up an entry in a dynroot directory.
140 */
141static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
142					 unsigned int flags)
143{
144	struct afs_vnode *vnode;
145	struct inode *inode;
146	int ret;
147
148	vnode = AFS_FS_I(dir);
149
150	_enter("%pd", dentry);
151
152	ASSERTCMP(d_inode(dentry), ==, NULL);
153
154	if (dentry->d_name.len >= AFSNAMEMAX) {
155		_leave(" = -ENAMETOOLONG");
156		return ERR_PTR(-ENAMETOOLONG);
157	}
158
159	if (dentry->d_name.len == 5 &&
160	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
161		return afs_lookup_atcell(dentry);
162
163	inode = afs_try_auto_mntpt(dentry, dir);
164	if (IS_ERR(inode)) {
165		ret = PTR_ERR(inode);
166		if (ret == -ENOENT) {
167			d_add(dentry, NULL);
168			_leave(" = NULL [negative]");
169			return NULL;
170		}
171		_leave(" = %d [do]", ret);
172		return ERR_PTR(ret);
173	}
174
175	d_add(dentry, inode);
176	_leave(" = 0 { ino=%lu v=%u }",
177	       d_inode(dentry)->i_ino, d_inode(dentry)->i_generation);
178	return NULL;
179}
180
181const struct inode_operations afs_dynroot_inode_operations = {
182	.lookup		= afs_dynroot_lookup,
183};
184
185/*
186 * Dirs in the dynamic root don't need revalidation.
187 */
188static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
189{
190	return 1;
191}
192
193/*
194 * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
195 * sleep)
196 * - called from dput() when d_count is going to 0.
197 * - return 1 to request dentry be unhashed, 0 otherwise
198 */
199static int afs_dynroot_d_delete(const struct dentry *dentry)
200{
201	return d_really_is_positive(dentry);
202}
203
204const struct dentry_operations afs_dynroot_dentry_operations = {
205	.d_revalidate	= afs_dynroot_d_revalidate,
206	.d_delete	= afs_dynroot_d_delete,
207	.d_release	= afs_d_release,
208	.d_automount	= afs_d_automount,
209};