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 | */ |
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, 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 | |
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(p: s, q: "../" ); |
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 | |
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(kn: parent); |
117 | int error; |
118 | |
119 | down_read(sem: &root->kernfs_rwsem); |
120 | error = kernfs_get_target_path(parent, target, path); |
121 | up_read(sem: &root->kernfs_rwsem); |
122 | |
123 | return error; |
124 | } |
125 | |
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(error: -ECHILD); |
135 | body = kzalloc(PAGE_SIZE, GFP_KERNEL); |
136 | if (!body) |
137 | return ERR_PTR(error: -ENOMEM); |
138 | error = kernfs_getlink(inode, path: body); |
139 | if (unlikely(error < 0)) { |
140 | kfree(objp: body); |
141 | return ERR_PTR(error); |
142 | } |
143 | set_delayed_call(call: done, fn: kfree_link, arg: 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 | |