fs/kernfs/symlink.c

   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 };