1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0-only
2*4882a593Smuzhiyun /*
3*4882a593Smuzhiyun * fs/kernfs/symlink.c - kernfs symlink implementation
4*4882a593Smuzhiyun *
5*4882a593Smuzhiyun * Copyright (c) 2001-3 Patrick Mochel
6*4882a593Smuzhiyun * Copyright (c) 2007 SUSE Linux Products GmbH
7*4882a593Smuzhiyun * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
8*4882a593Smuzhiyun */
9*4882a593Smuzhiyun
10*4882a593Smuzhiyun #include <linux/fs.h>
11*4882a593Smuzhiyun #include <linux/gfp.h>
12*4882a593Smuzhiyun #include <linux/namei.h>
13*4882a593Smuzhiyun
14*4882a593Smuzhiyun #include "kernfs-internal.h"
15*4882a593Smuzhiyun
16*4882a593Smuzhiyun /**
17*4882a593Smuzhiyun * kernfs_create_link - create a symlink
18*4882a593Smuzhiyun * @parent: directory to create the symlink in
19*4882a593Smuzhiyun * @name: name of the symlink
20*4882a593Smuzhiyun * @target: target node for the symlink to point to
21*4882a593Smuzhiyun *
22*4882a593Smuzhiyun * Returns the created node on success, ERR_PTR() value on error.
23*4882a593Smuzhiyun * Ownership of the link matches ownership of the target.
24*4882a593Smuzhiyun */
kernfs_create_link(struct kernfs_node * parent,const char * name,struct kernfs_node * target)25*4882a593Smuzhiyun struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
26*4882a593Smuzhiyun const char *name,
27*4882a593Smuzhiyun struct kernfs_node *target)
28*4882a593Smuzhiyun {
29*4882a593Smuzhiyun struct kernfs_node *kn;
30*4882a593Smuzhiyun int error;
31*4882a593Smuzhiyun kuid_t uid = GLOBAL_ROOT_UID;
32*4882a593Smuzhiyun kgid_t gid = GLOBAL_ROOT_GID;
33*4882a593Smuzhiyun
34*4882a593Smuzhiyun if (target->iattr) {
35*4882a593Smuzhiyun uid = target->iattr->ia_uid;
36*4882a593Smuzhiyun gid = target->iattr->ia_gid;
37*4882a593Smuzhiyun }
38*4882a593Smuzhiyun
39*4882a593Smuzhiyun kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, uid, gid,
40*4882a593Smuzhiyun KERNFS_LINK);
41*4882a593Smuzhiyun if (!kn)
42*4882a593Smuzhiyun return ERR_PTR(-ENOMEM);
43*4882a593Smuzhiyun
44*4882a593Smuzhiyun if (kernfs_ns_enabled(parent))
45*4882a593Smuzhiyun kn->ns = target->ns;
46*4882a593Smuzhiyun kn->symlink.target_kn = target;
47*4882a593Smuzhiyun kernfs_get(target); /* ref owned by symlink */
48*4882a593Smuzhiyun
49*4882a593Smuzhiyun error = kernfs_add_one(kn);
50*4882a593Smuzhiyun if (!error)
51*4882a593Smuzhiyun return kn;
52*4882a593Smuzhiyun
53*4882a593Smuzhiyun kernfs_put(kn);
54*4882a593Smuzhiyun return ERR_PTR(error);
55*4882a593Smuzhiyun }
56*4882a593Smuzhiyun
kernfs_get_target_path(struct kernfs_node * parent,struct kernfs_node * target,char * path)57*4882a593Smuzhiyun static int kernfs_get_target_path(struct kernfs_node *parent,
58*4882a593Smuzhiyun struct kernfs_node *target, char *path)
59*4882a593Smuzhiyun {
60*4882a593Smuzhiyun struct kernfs_node *base, *kn;
61*4882a593Smuzhiyun char *s = path;
62*4882a593Smuzhiyun int len = 0;
63*4882a593Smuzhiyun
64*4882a593Smuzhiyun /* go up to the root, stop at the base */
65*4882a593Smuzhiyun base = parent;
66*4882a593Smuzhiyun while (base->parent) {
67*4882a593Smuzhiyun kn = target->parent;
68*4882a593Smuzhiyun while (kn->parent && base != kn)
69*4882a593Smuzhiyun kn = kn->parent;
70*4882a593Smuzhiyun
71*4882a593Smuzhiyun if (base == kn)
72*4882a593Smuzhiyun break;
73*4882a593Smuzhiyun
74*4882a593Smuzhiyun if ((s - path) + 3 >= PATH_MAX)
75*4882a593Smuzhiyun return -ENAMETOOLONG;
76*4882a593Smuzhiyun
77*4882a593Smuzhiyun strcpy(s, "../");
78*4882a593Smuzhiyun s += 3;
79*4882a593Smuzhiyun base = base->parent;
80*4882a593Smuzhiyun }
81*4882a593Smuzhiyun
82*4882a593Smuzhiyun /* determine end of target string for reverse fillup */
83*4882a593Smuzhiyun kn = target;
84*4882a593Smuzhiyun while (kn->parent && kn != base) {
85*4882a593Smuzhiyun len += strlen(kn->name) + 1;
86*4882a593Smuzhiyun kn = kn->parent;
87*4882a593Smuzhiyun }
88*4882a593Smuzhiyun
89*4882a593Smuzhiyun /* check limits */
90*4882a593Smuzhiyun if (len < 2)
91*4882a593Smuzhiyun return -EINVAL;
92*4882a593Smuzhiyun len--;
93*4882a593Smuzhiyun if ((s - path) + len >= PATH_MAX)
94*4882a593Smuzhiyun return -ENAMETOOLONG;
95*4882a593Smuzhiyun
96*4882a593Smuzhiyun /* reverse fillup of target string from target to base */
97*4882a593Smuzhiyun kn = target;
98*4882a593Smuzhiyun while (kn->parent && kn != base) {
99*4882a593Smuzhiyun int slen = strlen(kn->name);
100*4882a593Smuzhiyun
101*4882a593Smuzhiyun len -= slen;
102*4882a593Smuzhiyun memcpy(s + len, kn->name, slen);
103*4882a593Smuzhiyun if (len)
104*4882a593Smuzhiyun s[--len] = '/';
105*4882a593Smuzhiyun
106*4882a593Smuzhiyun kn = kn->parent;
107*4882a593Smuzhiyun }
108*4882a593Smuzhiyun
109*4882a593Smuzhiyun return 0;
110*4882a593Smuzhiyun }
111*4882a593Smuzhiyun
kernfs_getlink(struct inode * inode,char * path)112*4882a593Smuzhiyun static int kernfs_getlink(struct inode *inode, char *path)
113*4882a593Smuzhiyun {
114*4882a593Smuzhiyun struct kernfs_node *kn = inode->i_private;
115*4882a593Smuzhiyun struct kernfs_node *parent = kn->parent;
116*4882a593Smuzhiyun struct kernfs_node *target = kn->symlink.target_kn;
117*4882a593Smuzhiyun int error;
118*4882a593Smuzhiyun
119*4882a593Smuzhiyun mutex_lock(&kernfs_mutex);
120*4882a593Smuzhiyun error = kernfs_get_target_path(parent, target, path);
121*4882a593Smuzhiyun mutex_unlock(&kernfs_mutex);
122*4882a593Smuzhiyun
123*4882a593Smuzhiyun return error;
124*4882a593Smuzhiyun }
125*4882a593Smuzhiyun
kernfs_iop_get_link(struct dentry * dentry,struct inode * inode,struct delayed_call * done)126*4882a593Smuzhiyun static const char *kernfs_iop_get_link(struct dentry *dentry,
127*4882a593Smuzhiyun struct inode *inode,
128*4882a593Smuzhiyun struct delayed_call *done)
129*4882a593Smuzhiyun {
130*4882a593Smuzhiyun char *body;
131*4882a593Smuzhiyun int error;
132*4882a593Smuzhiyun
133*4882a593Smuzhiyun if (!dentry)
134*4882a593Smuzhiyun return ERR_PTR(-ECHILD);
135*4882a593Smuzhiyun body = kzalloc(PAGE_SIZE, GFP_KERNEL);
136*4882a593Smuzhiyun if (!body)
137*4882a593Smuzhiyun return ERR_PTR(-ENOMEM);
138*4882a593Smuzhiyun error = kernfs_getlink(inode, body);
139*4882a593Smuzhiyun if (unlikely(error < 0)) {
140*4882a593Smuzhiyun kfree(body);
141*4882a593Smuzhiyun return ERR_PTR(error);
142*4882a593Smuzhiyun }
143*4882a593Smuzhiyun set_delayed_call(done, kfree_link, body);
144*4882a593Smuzhiyun return body;
145*4882a593Smuzhiyun }
146*4882a593Smuzhiyun
147*4882a593Smuzhiyun const struct inode_operations kernfs_symlink_iops = {
148*4882a593Smuzhiyun .listxattr = kernfs_iop_listxattr,
149*4882a593Smuzhiyun .get_link = kernfs_iop_get_link,
150*4882a593Smuzhiyun .setattr = kernfs_iop_setattr,
151*4882a593Smuzhiyun .getattr = kernfs_iop_getattr,
152*4882a593Smuzhiyun .permission = kernfs_iop_permission,
153*4882a593Smuzhiyun };
154