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 (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(s, "../"); 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(parent); 117 int error; 118 119 down_read(&root->kernfs_rwsem); 120 error = kernfs_get_target_path(parent, target, path); 121 up_read(&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(-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 } 146 147 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