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 * Ownership of the link matches ownership of the target. 25 */ 26 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent, 27 const char *name, 28 struct kernfs_node *target) 29 { 30 struct kernfs_node *kn; 31 int error; 32 kuid_t uid = GLOBAL_ROOT_UID; 33 kgid_t gid = GLOBAL_ROOT_GID; 34 35 if (target->iattr) { 36 uid = target->iattr->ia_iattr.ia_uid; 37 gid = target->iattr->ia_iattr.ia_gid; 38 } 39 40 kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, uid, gid, 41 KERNFS_LINK); 42 if (!kn) 43 return ERR_PTR(-ENOMEM); 44 45 if (kernfs_ns_enabled(parent)) 46 kn->ns = target->ns; 47 kn->symlink.target_kn = target; 48 kernfs_get(target); /* ref owned by symlink */ 49 50 error = kernfs_add_one(kn); 51 if (!error) 52 return kn; 53 54 kernfs_put(kn); 55 return ERR_PTR(error); 56 } 57 58 static int kernfs_get_target_path(struct kernfs_node *parent, 59 struct kernfs_node *target, char *path) 60 { 61 struct kernfs_node *base, *kn; 62 char *s = path; 63 int len = 0; 64 65 /* go up to the root, stop at the base */ 66 base = parent; 67 while (base->parent) { 68 kn = target->parent; 69 while (kn->parent && base != kn) 70 kn = kn->parent; 71 72 if (base == kn) 73 break; 74 75 strcpy(s, "../"); 76 s += 3; 77 base = base->parent; 78 } 79 80 /* determine end of target string for reverse fillup */ 81 kn = target; 82 while (kn->parent && kn != base) { 83 len += strlen(kn->name) + 1; 84 kn = kn->parent; 85 } 86 87 /* check limits */ 88 if (len < 2) 89 return -EINVAL; 90 len--; 91 if ((s - path) + len > PATH_MAX) 92 return -ENAMETOOLONG; 93 94 /* reverse fillup of target string from target to base */ 95 kn = target; 96 while (kn->parent && kn != base) { 97 int slen = strlen(kn->name); 98 99 len -= slen; 100 memcpy(s + len, kn->name, slen); 101 if (len) 102 s[--len] = '/'; 103 104 kn = kn->parent; 105 } 106 107 return 0; 108 } 109 110 static int kernfs_getlink(struct inode *inode, char *path) 111 { 112 struct kernfs_node *kn = inode->i_private; 113 struct kernfs_node *parent = kn->parent; 114 struct kernfs_node *target = kn->symlink.target_kn; 115 int error; 116 117 mutex_lock(&kernfs_mutex); 118 error = kernfs_get_target_path(parent, target, path); 119 mutex_unlock(&kernfs_mutex); 120 121 return error; 122 } 123 124 static const char *kernfs_iop_get_link(struct dentry *dentry, 125 struct inode *inode, 126 struct delayed_call *done) 127 { 128 char *body; 129 int error; 130 131 if (!dentry) 132 return ERR_PTR(-ECHILD); 133 body = kzalloc(PAGE_SIZE, GFP_KERNEL); 134 if (!body) 135 return ERR_PTR(-ENOMEM); 136 error = kernfs_getlink(inode, body); 137 if (unlikely(error < 0)) { 138 kfree(body); 139 return ERR_PTR(error); 140 } 141 set_delayed_call(done, kfree_link, body); 142 return body; 143 } 144 145 const struct inode_operations kernfs_symlink_iops = { 146 .listxattr = kernfs_iop_listxattr, 147 .get_link = kernfs_iop_get_link, 148 .setattr = kernfs_iop_setattr, 149 .getattr = kernfs_iop_getattr, 150 .permission = kernfs_iop_permission, 151 }; 152