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 * Returns 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|S_IRWXUGO, uid, gid,
 40			     KERNFS_LINK);
 41	if (!kn)
 42		return ERR_PTR(-ENOMEM);
 43
 44	if (kernfs_ns_enabled(parent))
 45		kn->ns = target->ns;
 46	kn->symlink.target_kn = target;
 47	kernfs_get(target);	/* ref owned by symlink */
 48
 49	error = kernfs_add_one(kn);
 50	if (!error)
 51		return kn;
 52
 53	kernfs_put(kn);
 54	return ERR_PTR(error);
 55}
 56
 57static int kernfs_get_target_path(struct kernfs_node *parent,
 58				  struct kernfs_node *target, char *path)
 59{
 60	struct kernfs_node *base, *kn;
 61	char *s = path;
 62	int len = 0;
 63
 64	/* go up to the root, stop at the base */
 65	base = parent;
 66	while (base->parent) {
 67		kn = target->parent;
 68		while (kn->parent && base != kn)
 69			kn = kn->parent;
 70
 71		if (base == kn)
 72			break;
 73
 74		if ((s - path) + 3 >= PATH_MAX)
 75			return -ENAMETOOLONG;
 76
 77		strcpy(s, "../");
 78		s += 3;
 79		base = base->parent;
 80	}
 81
 82	/* determine end of target string for reverse fillup */
 83	kn = target;
 84	while (kn->parent && kn != base) {
 85		len += strlen(kn->name) + 1;
 86		kn = kn->parent;
 87	}
 88
 89	/* check limits */
 90	if (len < 2)
 91		return -EINVAL;
 92	len--;
 93	if ((s - path) + len >= PATH_MAX)
 94		return -ENAMETOOLONG;
 95
 96	/* reverse fillup of target string from target to base */
 97	kn = target;
 98	while (kn->parent && kn != base) {
 99		int slen = strlen(kn->name);
100
101		len -= slen;
102		memcpy(s + len, kn->name, slen);
103		if (len)
104			s[--len] = '/';
105
106		kn = kn->parent;
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 = kn->parent;
116	struct kernfs_node *target = kn->symlink.target_kn;
117	int error;
118
119	mutex_lock(&kernfs_mutex);
120	error = kernfs_get_target_path(parent, target, path);
121	mutex_unlock(&kernfs_mutex);
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};

 
  1/*
  2 * fs/kernfs/symlink.c - kernfs symlink implementation
  3 *
  4 * Copyright (c) 2001-3 Patrick Mochel
  5 * Copyright (c) 2007 SUSE Linux Products GmbH
  6 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  7 *
  8 * This file is released under the GPLv2.
  9 */
 10
 11#include <linux/fs.h>
 12#include <linux/gfp.h>
 13#include <linux/namei.h>
 14
 15#include "kernfs-internal.h"
 16
 17/**
 18 * kernfs_create_link - create a symlink
 19 * @parent: directory to create the symlink in
 20 * @name: name of the symlink
 21 * @target: target node for the symlink to point to
 22 *
 23 * Returns the created node on success, ERR_PTR() value on error.
 
 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
 32	kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, KERNFS_LINK);
 
 33	if (!kn)
 34		return ERR_PTR(-ENOMEM);
 35
 36	if (kernfs_ns_enabled(parent))
 37		kn->ns = target->ns;
 38	kn->symlink.target_kn = target;
 39	kernfs_get(target);	/* ref owned by symlink */
 40
 41	error = kernfs_add_one(kn);
 42	if (!error)
 43		return kn;
 44
 45	kernfs_put(kn);
 46	return ERR_PTR(error);
 47}
 48
 49static int kernfs_get_target_path(struct kernfs_node *parent,
 50				  struct kernfs_node *target, char *path)
 51{
 52	struct kernfs_node *base, *kn;
 53	char *s = path;
 54	int len = 0;
 55
 56	/* go up to the root, stop at the base */
 57	base = parent;
 58	while (base->parent) {
 59		kn = target->parent;
 60		while (kn->parent && base != kn)
 61			kn = kn->parent;
 62
 63		if (base == kn)
 64			break;
 65
 
 
 
 66		strcpy(s, "../");
 67		s += 3;
 68		base = base->parent;
 69	}
 70
 71	/* determine end of target string for reverse fillup */
 72	kn = target;
 73	while (kn->parent && kn != base) {
 74		len += strlen(kn->name) + 1;
 75		kn = kn->parent;
 76	}
 77
 78	/* check limits */
 79	if (len < 2)
 80		return -EINVAL;
 81	len--;
 82	if ((s - path) + len > PATH_MAX)
 83		return -ENAMETOOLONG;
 84
 85	/* reverse fillup of target string from target to base */
 86	kn = target;
 87	while (kn->parent && kn != base) {
 88		int slen = strlen(kn->name);
 89
 90		len -= slen;
 91		strncpy(s + len, kn->name, slen);
 92		if (len)
 93			s[--len] = '/';
 94
 95		kn = kn->parent;
 96	}
 97
 98	return 0;
 99}
100
101static int kernfs_getlink(struct dentry *dentry, char *path)
102{
103	struct kernfs_node *kn = dentry->d_fsdata;
104	struct kernfs_node *parent = kn->parent;
105	struct kernfs_node *target = kn->symlink.target_kn;
106	int error;
107
108	mutex_lock(&kernfs_mutex);
109	error = kernfs_get_target_path(parent, target, path);
110	mutex_unlock(&kernfs_mutex);
111
112	return error;
113}
114
115static void *kernfs_iop_follow_link(struct dentry *dentry, struct nameidata *nd)
 
 
116{
117	int error = -ENOMEM;
118	unsigned long page = get_zeroed_page(GFP_KERNEL);
119	if (page) {
120		error = kernfs_getlink(dentry, (char *) page);
121		if (error < 0)
122			free_page((unsigned long)page);
 
 
 
 
 
 
123	}
124	nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
125	return NULL;
126}
127
128static void kernfs_iop_put_link(struct dentry *dentry, struct nameidata *nd,
129				void *cookie)
130{
131	char *page = nd_get_link(nd);
132	if (!IS_ERR(page))
133		free_page((unsigned long)page);
134}
135
136const struct inode_operations kernfs_symlink_iops = {
137	.setxattr	= kernfs_iop_setxattr,
138	.removexattr	= kernfs_iop_removexattr,
139	.getxattr	= kernfs_iop_getxattr,
140	.listxattr	= kernfs_iop_listxattr,
141	.readlink	= generic_readlink,
142	.follow_link	= kernfs_iop_follow_link,
143	.put_link	= kernfs_iop_put_link,
144	.setattr	= kernfs_iop_setattr,
145	.getattr	= kernfs_iop_getattr,
146	.permission	= kernfs_iop_permission,
147};