1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * V9FS FID Management
4 *
5 * Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
6 * Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
7 */
8
9 #include <linux/module.h>
10 #include <linux/errno.h>
11 #include <linux/fs.h>
12 #include <linux/slab.h>
13 #include <linux/sched.h>
14 #include <linux/idr.h>
15 #include <net/9p/9p.h>
16 #include <net/9p/client.h>
17
18 #include "v9fs.h"
19 #include "v9fs_vfs.h"
20 #include "fid.h"
21
22 /**
23 * v9fs_fid_add - add a fid to a dentry
24 * @dentry: dentry that the fid is being added to
25 * @fid: fid to add
26 *
27 */
28
__add_fid(struct dentry * dentry,struct p9_fid * fid)29 static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
30 {
31 hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
32 }
33
v9fs_fid_add(struct dentry * dentry,struct p9_fid * fid)34 void v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
35 {
36 spin_lock(&dentry->d_lock);
37 __add_fid(dentry, fid);
38 spin_unlock(&dentry->d_lock);
39 }
40
41 /**
42 * v9fs_fid_find - retrieve a fid that belongs to the specified uid
43 * @dentry: dentry to look for fid in
44 * @uid: return fid that belongs to the specified user
45 * @any: if non-zero, return any fid associated with the dentry
46 *
47 */
48
v9fs_fid_find(struct dentry * dentry,kuid_t uid,int any)49 static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
50 {
51 struct p9_fid *fid, *ret;
52
53 p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p) uid %d any %d\n",
54 dentry, dentry, from_kuid(&init_user_ns, uid),
55 any);
56 ret = NULL;
57 /* we'll recheck under lock if there's anything to look in */
58 if (dentry->d_fsdata) {
59 struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
60 spin_lock(&dentry->d_lock);
61 hlist_for_each_entry(fid, h, dlist) {
62 if (any || uid_eq(fid->uid, uid)) {
63 ret = fid;
64 break;
65 }
66 }
67 spin_unlock(&dentry->d_lock);
68 }
69
70 return ret;
71 }
72
73 /*
74 * We need to hold v9ses->rename_sem as long as we hold references
75 * to returned path array. Array element contain pointers to
76 * dentry names.
77 */
build_path_from_dentry(struct v9fs_session_info * v9ses,struct dentry * dentry,const unsigned char *** names)78 static int build_path_from_dentry(struct v9fs_session_info *v9ses,
79 struct dentry *dentry, const unsigned char ***names)
80 {
81 int n = 0, i;
82 const unsigned char **wnames;
83 struct dentry *ds;
84
85 for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
86 n++;
87
88 wnames = kmalloc_array(n, sizeof(char *), GFP_KERNEL);
89 if (!wnames)
90 goto err_out;
91
92 for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
93 wnames[i] = ds->d_name.name;
94
95 *names = wnames;
96 return n;
97 err_out:
98 return -ENOMEM;
99 }
100
v9fs_fid_lookup_with_uid(struct dentry * dentry,kuid_t uid,int any)101 static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
102 kuid_t uid, int any)
103 {
104 struct dentry *ds;
105 const unsigned char **wnames, *uname;
106 int i, n, l, clone, access;
107 struct v9fs_session_info *v9ses;
108 struct p9_fid *fid, *old_fid = NULL;
109
110 v9ses = v9fs_dentry2v9ses(dentry);
111 access = v9ses->flags & V9FS_ACCESS_MASK;
112 fid = v9fs_fid_find(dentry, uid, any);
113 if (fid)
114 return fid;
115 /*
116 * we don't have a matching fid. To do a TWALK we need
117 * parent fid. We need to prevent rename when we want to
118 * look at the parent.
119 */
120 down_read(&v9ses->rename_sem);
121 ds = dentry->d_parent;
122 fid = v9fs_fid_find(ds, uid, any);
123 if (fid) {
124 /* Found the parent fid do a lookup with that */
125 fid = p9_client_walk(fid, 1, &dentry->d_name.name, 1);
126 goto fid_out;
127 }
128 up_read(&v9ses->rename_sem);
129
130 /* start from the root and try to do a lookup */
131 fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
132 if (!fid) {
133 /* the user is not attached to the fs yet */
134 if (access == V9FS_ACCESS_SINGLE)
135 return ERR_PTR(-EPERM);
136
137 if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
138 uname = NULL;
139 else
140 uname = v9ses->uname;
141
142 fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
143 v9ses->aname);
144 if (IS_ERR(fid))
145 return fid;
146
147 v9fs_fid_add(dentry->d_sb->s_root, fid);
148 }
149 /* If we are root ourself just return that */
150 if (dentry->d_sb->s_root == dentry)
151 return fid;
152 /*
153 * Do a multipath walk with attached root.
154 * When walking parent we need to make sure we
155 * don't have a parallel rename happening
156 */
157 down_read(&v9ses->rename_sem);
158 n = build_path_from_dentry(v9ses, dentry, &wnames);
159 if (n < 0) {
160 fid = ERR_PTR(n);
161 goto err_out;
162 }
163 clone = 1;
164 i = 0;
165 while (i < n) {
166 l = min(n - i, P9_MAXWELEM);
167 /*
168 * We need to hold rename lock when doing a multipath
169 * walk to ensure none of the patch component change
170 */
171 fid = p9_client_walk(fid, l, &wnames[i], clone);
172 if (IS_ERR(fid)) {
173 if (old_fid) {
174 /*
175 * If we fail, clunk fid which are mapping
176 * to path component and not the last component
177 * of the path.
178 */
179 p9_client_clunk(old_fid);
180 }
181 kfree(wnames);
182 goto err_out;
183 }
184 old_fid = fid;
185 i += l;
186 clone = 0;
187 }
188 kfree(wnames);
189 fid_out:
190 if (!IS_ERR(fid)) {
191 spin_lock(&dentry->d_lock);
192 if (d_unhashed(dentry)) {
193 spin_unlock(&dentry->d_lock);
194 p9_client_clunk(fid);
195 fid = ERR_PTR(-ENOENT);
196 } else {
197 __add_fid(dentry, fid);
198 spin_unlock(&dentry->d_lock);
199 }
200 }
201 err_out:
202 up_read(&v9ses->rename_sem);
203 return fid;
204 }
205
206 /**
207 * v9fs_fid_lookup - lookup for a fid, try to walk if not found
208 * @dentry: dentry to look for fid in
209 *
210 * Look for a fid in the specified dentry for the current user.
211 * If no fid is found, try to create one walking from a fid from the parent
212 * dentry (if it has one), or the root dentry. If the user haven't accessed
213 * the fs yet, attach now and walk from the root.
214 */
215
v9fs_fid_lookup(struct dentry * dentry)216 struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
217 {
218 kuid_t uid;
219 int any, access;
220 struct v9fs_session_info *v9ses;
221
222 v9ses = v9fs_dentry2v9ses(dentry);
223 access = v9ses->flags & V9FS_ACCESS_MASK;
224 switch (access) {
225 case V9FS_ACCESS_SINGLE:
226 case V9FS_ACCESS_USER:
227 case V9FS_ACCESS_CLIENT:
228 uid = current_fsuid();
229 any = 0;
230 break;
231
232 case V9FS_ACCESS_ANY:
233 uid = v9ses->uid;
234 any = 1;
235 break;
236
237 default:
238 uid = INVALID_UID;
239 any = 0;
240 break;
241 }
242 return v9fs_fid_lookup_with_uid(dentry, uid, any);
243 }
244
v9fs_writeback_fid(struct dentry * dentry)245 struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
246 {
247 int err;
248 struct p9_fid *fid;
249
250 fid = clone_fid(v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0));
251 if (IS_ERR(fid))
252 goto error_out;
253 /*
254 * writeback fid will only be used to write back the
255 * dirty pages. We always request for the open fid in read-write
256 * mode so that a partial page write which result in page
257 * read can work.
258 */
259 err = p9_client_open(fid, O_RDWR);
260 if (err < 0) {
261 p9_client_clunk(fid);
262 fid = ERR_PTR(err);
263 goto error_out;
264 }
265 error_out:
266 return fid;
267 }
268