1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 *   Contains the CIFS DFS referral mounting routines used for handling
  4 *   traversal via DFS junction point
  5 *
  6 *   Copyright (c) 2007 Igor Mammedov
  7 *   Copyright (C) International Business Machines  Corp., 2008
  8 *   Author(s): Igor Mammedov (niallain@gmail.com)
  9 *		Steve French (sfrench@us.ibm.com)
 10 */
 11
 12#include <linux/dcache.h>
 13#include <linux/mount.h>
 14#include <linux/namei.h>
 15#include <linux/slab.h>
 16#include <linux/vfs.h>
 17#include <linux/fs.h>
 18#include <linux/inet.h>
 19#include "cifsglob.h"
 20#include "cifsproto.h"
 21#include "cifsfs.h"
 22#include "dns_resolve.h"
 23#include "cifs_debug.h"
 24#include "dfs.h"
 25#include "fs_context.h"
 26
 27static LIST_HEAD(cifs_dfs_automount_list);
 28
 29static void cifs_dfs_expire_automounts(struct work_struct *work);
 30static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
 31			    cifs_dfs_expire_automounts);
 32static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;
 33
 34static void cifs_dfs_expire_automounts(struct work_struct *work)
 35{
 36	struct list_head *list = &cifs_dfs_automount_list;
 37
 38	mark_mounts_for_expiry(list);
 39	if (!list_empty(list))
 40		schedule_delayed_work(&cifs_dfs_automount_task,
 41				      cifs_dfs_mountpoint_expiry_timeout);
 42}
 43
 44void cifs_dfs_release_automount_timer(void)
 45{
 46	BUG_ON(!list_empty(&cifs_dfs_automount_list));
 47	cancel_delayed_work_sync(&cifs_dfs_automount_task);
 48}
 49
 50/**
 51 * cifs_build_devname - build a devicename from a UNC and optional prepath
 52 * @nodename:	pointer to UNC string
 53 * @prepath:	pointer to prefixpath (or NULL if there isn't one)
 54 *
 55 * Build a new cifs devicename after chasing a DFS referral. Allocate a buffer
 56 * big enough to hold the final thing. Copy the UNC from the nodename, and
 57 * concatenate the prepath onto the end of it if there is one.
 58 *
 59 * Returns pointer to the built string, or a ERR_PTR. Caller is responsible
 60 * for freeing the returned string.
 61 */
 62char *
 63cifs_build_devname(char *nodename, const char *prepath)
 64{
 65	size_t pplen;
 66	size_t unclen;
 67	char *dev;
 68	char *pos;
 69
 70	/* skip over any preceding delimiters */
 71	nodename += strspn(nodename, "\\");
 72	if (!*nodename)
 73		return ERR_PTR(-EINVAL);
 74
 75	/* get length of UNC and set pos to last char */
 76	unclen = strlen(nodename);
 77	pos = nodename + unclen - 1;
 78
 79	/* trim off any trailing delimiters */
 80	while (*pos == '\\') {
 81		--pos;
 82		--unclen;
 83	}
 84
 85	/* allocate a buffer:
 86	 * +2 for preceding "//"
 87	 * +1 for delimiter between UNC and prepath
 88	 * +1 for trailing NULL
 89	 */
 90	pplen = prepath ? strlen(prepath) : 0;
 91	dev = kmalloc(2 + unclen + 1 + pplen + 1, GFP_KERNEL);
 92	if (!dev)
 93		return ERR_PTR(-ENOMEM);
 94
 95	pos = dev;
 96	/* add the initial "//" */
 97	*pos = '/';
 98	++pos;
 99	*pos = '/';
100	++pos;
101
102	/* copy in the UNC portion from referral */
103	memcpy(pos, nodename, unclen);
104	pos += unclen;
105
106	/* copy the prefixpath remainder (if there is one) */
107	if (pplen) {
108		*pos = '/';
109		++pos;
110		memcpy(pos, prepath, pplen);
111		pos += pplen;
112	}
113
114	/* NULL terminator */
115	*pos = '\0';
116
117	convert_delimiter(dev, '/');
118	return dev;
119}
120
121static int set_dest_addr(struct smb3_fs_context *ctx, const char *full_path)
122{
123	struct sockaddr *addr = (struct sockaddr *)&ctx->dstaddr;
124	int rc;
125
126	rc = dns_resolve_server_name_to_ip(full_path, addr, NULL);
127	if (!rc)
128		cifs_set_port(addr, ctx->port);
129	return rc;
130}
131
132/*
133 * Create a vfsmount that we can automount
134 */
135static struct vfsmount *cifs_dfs_do_automount(struct path *path)
136{
137	int rc;
138	struct dentry *mntpt = path->dentry;
139	struct fs_context *fc;
140	struct cifs_sb_info *cifs_sb;
141	void *page = NULL;
142	struct smb3_fs_context *ctx, *cur_ctx;
143	struct smb3_fs_context tmp;
144	char *full_path;
145	struct vfsmount *mnt;
146
147	if (IS_ROOT(mntpt))
148		return ERR_PTR(-ESTALE);
149
150	/*
151	 * The MSDFS spec states that paths in DFS referral requests and
152	 * responses must be prefixed by a single '\' character instead of
153	 * the double backslashes usually used in the UNC. This function
154	 * gives us the latter, so we must adjust the result.
155	 */
156	cifs_sb = CIFS_SB(mntpt->d_sb);
157	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS)
158		return ERR_PTR(-EREMOTE);
159
160	cur_ctx = cifs_sb->ctx;
161
162	fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, mntpt);
163	if (IS_ERR(fc))
164		return ERR_CAST(fc);
165
166	ctx = smb3_fc2context(fc);
167
168	page = alloc_dentry_path();
169	full_path = dfs_get_automount_devname(mntpt, page);
170	if (IS_ERR(full_path)) {
171		mnt = ERR_CAST(full_path);
172		goto out;
173	}
174
175	convert_delimiter(full_path, '/');
176	cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
177
178	tmp = *cur_ctx;
179	tmp.source = full_path;
180	tmp.leaf_fullpath = NULL;
181	tmp.UNC = tmp.prepath = NULL;
182
183	rc = smb3_fs_context_dup(ctx, &tmp);
184	if (rc) {
185		mnt = ERR_PTR(rc);
186		goto out;
187	}
188
189	rc = set_dest_addr(ctx, full_path);
190	if (rc) {
191		mnt = ERR_PTR(rc);
192		goto out;
193	}
194
195	rc = smb3_parse_devname(full_path, ctx);
196	if (!rc)
197		mnt = fc_mount(fc);
198	else
199		mnt = ERR_PTR(rc);
200
201out:
202	put_fs_context(fc);
203	free_dentry_path(page);
204	return mnt;
205}
206
207/*
208 * Attempt to automount the referral
209 */
210struct vfsmount *cifs_dfs_d_automount(struct path *path)
211{
212	struct vfsmount *newmnt;
213
214	cifs_dbg(FYI, "%s: %pd\n", __func__, path->dentry);
215
216	newmnt = cifs_dfs_do_automount(path);
217	if (IS_ERR(newmnt)) {
218		cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
219		return newmnt;
220	}
221
222	mntget(newmnt); /* prevent immediate expiration */
223	mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
224	schedule_delayed_work(&cifs_dfs_automount_task,
225			      cifs_dfs_mountpoint_expiry_timeout);
226	cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
227	return newmnt;
228}
229
230const struct inode_operations cifs_dfs_referral_inode_operations = {
231};