symlink.c

  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 (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
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(&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
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(-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
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};