fs/kernfs/symlink.c

   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 };