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 (kernfs_parent(base)) {
66 kn = kernfs_parent(target);
67 while (kernfs_parent(kn) && base != kn)
68 kn = kernfs_parent(kn);
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 = kernfs_parent(base);
79 }
80
81 /* determine end of target string for reverse fillup */
82 kn = target;
83 while (kernfs_parent(kn) && kn != base) {
84 len += strlen(kernfs_rcu_name(kn)) + 1;
85 kn = kernfs_parent(kn);
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 (kernfs_parent(kn) && kn != base) {
98 const char *name = kernfs_rcu_name(kn);
99 int slen = strlen(name);
100
101 len -= slen;
102 memcpy(s + len, name, slen);
103 if (len)
104 s[--len] = '/';
105
106 kn = kernfs_parent(kn);
107 }
108
109 return 0;
110 }
111
kernfs_getlink(struct inode * inode,char * path)112 static int kernfs_getlink(struct inode *inode, char *path)
113 {
114 struct kernfs_node *kn = inode->i_private;
115 struct kernfs_node *parent;
116 struct kernfs_node *target = kn->symlink.target_kn;
117 struct kernfs_root *root = kernfs_root(kn);
118 int error;
119
120 down_read(&root->kernfs_rwsem);
121 parent = kernfs_parent(kn);
122 error = kernfs_get_target_path(parent, target, path);
123 up_read(&root->kernfs_rwsem);
124
125 return error;
126 }
127
kernfs_iop_get_link(struct dentry * dentry,struct inode * inode,struct delayed_call * done)128 static const char *kernfs_iop_get_link(struct dentry *dentry,
129 struct inode *inode,
130 struct delayed_call *done)
131 {
132 char *body;
133 int error;
134
135 if (!dentry)
136 return ERR_PTR(-ECHILD);
137 body = kzalloc(PAGE_SIZE, GFP_KERNEL);
138 if (!body)
139 return ERR_PTR(-ENOMEM);
140 error = kernfs_getlink(inode, body);
141 if (unlikely(error < 0)) {
142 kfree(body);
143 return ERR_PTR(error);
144 }
145 set_delayed_call(done, kfree_link, body);
146 return body;
147 }
148
149 const struct inode_operations kernfs_symlink_iops = {
150 .listxattr = kernfs_iop_listxattr,
151 .get_link = kernfs_iop_get_link,
152 .setattr = kernfs_iop_setattr,
153 .getattr = kernfs_iop_getattr,
154 .permission = kernfs_iop_permission,
155 };
156