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 */
25struct 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, flags: KERNFS_LINK);
40 if (!kn)
41 return ERR_PTR(error: -ENOMEM);
42
43 if (kernfs_ns_enabled(kn: parent))
44 kn->ns = target->ns;
45 kn->symlink.target_kn = target;
46 kernfs_get(kn: 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
56static 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(kn: base)) {
66 kn = kernfs_parent(kn: 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(kn: 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(to: s + len, from: name, len: slen);
103 if (len)
104 s[--len] = '/';
105
106 kn = kernfs_parent(kn);
107 }
108
109 return 0;
110}
111
112static 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(sem: &root->kernfs_rwsem);
121 parent = kernfs_parent(kn);
122 error = kernfs_get_target_path(parent, target, path);
123 up_read(sem: &root->kernfs_rwsem);
124
125 return error;
126}
127
128static 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(error: -ECHILD);
137 body = kzalloc(PAGE_SIZE, GFP_KERNEL);
138 if (!body)
139 return ERR_PTR(error: -ENOMEM);
140 error = kernfs_getlink(inode, path: body);
141 if (unlikely(error < 0)) {
142 kfree(objp: body);
143 return ERR_PTR(error);
144 }
145 set_delayed_call(call: done, fn: kfree_link, arg: body);
146 return body;
147}
148
149const 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