1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * fs/kernfs/symlink.c - kernfs symlink implementation
4 *
5 * Copyright (c) 2001-3 Patrick Mochel
6 * Copyright (c) 2007 SUSE Linux Products GmbH
7 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
8 */
9
10 #include <linux/fs.h>
11 #include <linux/gfp.h>
12 #include <linux/namei.h>
13
14 #include "kernfs-internal.h"
15
16 /**
17 * kernfs_create_link - create a symlink
18 * @parent: directory to create the symlink in
19 * @name: name of the symlink
20 * @target: target node for the symlink to point to
21 *
22 * Return: the created node on success, ERR_PTR() value on error.
23 * Ownership of the link matches ownership of the target.
24 */
kernfs_create_link(struct kernfs_node * parent,const char * name,struct kernfs_node * target)25 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
26 const char *name,
27 struct kernfs_node *target)
28 {
29 struct kernfs_node *kn;
30 int error;
31 kuid_t uid = GLOBAL_ROOT_UID;
32 kgid_t gid = GLOBAL_ROOT_GID;
33
34 if (target->iattr) {
35 uid = target->iattr->ia_uid;
36 gid = target->iattr->ia_gid;
37 }
38
39 kn = kernfs_new_node(parent, name, S_IFLNK|0777, uid, gid, KERNFS_LINK);
40 if (!kn)
41 return ERR_PTR(-ENOMEM);
42
43 if (kernfs_ns_enabled(parent))
44 kn->ns = target->ns;
45 kn->symlink.target_kn = target;
46 kernfs_get(target); /* ref owned by symlink */
47
48 error = kernfs_add_one(kn);
49 if (!error)
50 return kn;
51
52 kernfs_put(kn);
53 return ERR_PTR(error);
54 }
55
kernfs_get_target_path(struct kernfs_node * parent,struct kernfs_node * target,char * path)56 static int kernfs_get_target_path(struct kernfs_node *parent,
57 struct kernfs_node *target, char *path)
58 {
59 struct kernfs_node *base, *kn;
60 char *s = path;
61 int len = 0;
62
63 /* go up to the root, stop at the base */
64 base = parent;
65 while (base->parent) {
66 kn = target->parent;
67 while (kn->parent && base != kn)
68 kn = kn->parent;
69
70 if (base == kn)
71 break;
72
73 if ((s - path) + 3 >= PATH_MAX)
74 return -ENAMETOOLONG;
75
76 strcpy(s, "../");
77 s += 3;
78 base = base->parent;
79 }
80
81 /* determine end of target string for reverse fillup */
82 kn = target;
83 while (kn->parent && kn != base) {
84 len += strlen(kn->name) + 1;
85 kn = kn->parent;
86 }
87
88 /* check limits */
89 if (len < 2)
90 return -EINVAL;
91 len--;
92 if ((s - path) + len >= PATH_MAX)
93 return -ENAMETOOLONG;
94
95 /* reverse fillup of target string from target to base */
96 kn = target;
97 while (kn->parent && kn != base) {
98 int slen = strlen(kn->name);
99
100 len -= slen;
101 memcpy(s + len, kn->name, slen);
102 if (len)
103 s[--len] = '/';
104
105 kn = kn->parent;
106 }
107
108 return 0;
109 }
110
kernfs_getlink(struct inode * inode,char * path)111 static int kernfs_getlink(struct inode *inode, char *path)
112 {
113 struct kernfs_node *kn = inode->i_private;
114 struct kernfs_node *parent = kn->parent;
115 struct kernfs_node *target = kn->symlink.target_kn;
116 struct kernfs_root *root = kernfs_root(parent);
117 int error;
118
119 down_read(&root->kernfs_rwsem);
120 error = kernfs_get_target_path(parent, target, path);
121 up_read(&root->kernfs_rwsem);
122
123 return error;
124 }
125
kernfs_iop_get_link(struct dentry * dentry,struct inode * inode,struct delayed_call * done)126 static const char *kernfs_iop_get_link(struct dentry *dentry,
127 struct inode *inode,
128 struct delayed_call *done)
129 {
130 char *body;
131 int error;
132
133 if (!dentry)
134 return ERR_PTR(-ECHILD);
135 body = kzalloc(PAGE_SIZE, GFP_KERNEL);
136 if (!body)
137 return ERR_PTR(-ENOMEM);
138 error = kernfs_getlink(inode, body);
139 if (unlikely(error < 0)) {
140 kfree(body);
141 return ERR_PTR(error);
142 }
143 set_delayed_call(done, kfree_link, body);
144 return body;
145 }
146
147 const struct inode_operations kernfs_symlink_iops = {
148 .listxattr = kernfs_iop_listxattr,
149 .get_link = kernfs_iop_get_link,
150 .setattr = kernfs_iop_setattr,
151 .getattr = kernfs_iop_getattr,
152 .permission = kernfs_iop_permission,
153 };
154