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
27 static LIST_HEAD(cifs_dfs_automount_list);
28
29 static void cifs_dfs_expire_automounts(struct work_struct *work);
30 static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
31 cifs_dfs_expire_automounts);
32 static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;
33
cifs_dfs_expire_automounts(struct work_struct * work)34 static 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
cifs_dfs_release_automount_timer(void)44 void 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 */
62 char *
cifs_build_devname(char * nodename,const char * prepath)63 cifs_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
set_dest_addr(struct smb3_fs_context * ctx,const char * full_path)121 static 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 */
cifs_dfs_do_automount(struct path * path)135 static 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
201 out:
202 put_fs_context(fc);
203 free_dentry_path(page);
204 return mnt;
205 }
206
207 /*
208 * Attempt to automount the referral
209 */
cifs_dfs_d_automount(struct path * path)210 struct 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
230 const struct inode_operations cifs_dfs_referral_inode_operations = {
231 };
232