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, 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
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 (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
111static 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
126static 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
147const 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