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, 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 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 (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 } 111 112 static 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 } 127 128 static 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 } 148 149 const 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 }; 156