LXR linux/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 * Returns the created node on success, ERR_PTR() value on error.
  23 * Ownership of the link matches ownership of the target.
  24 */
  25struct 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|S_IRWXUGO, uid, gid,
  40                             KERNFS_LINK);
  41        if (!kn)
  42                return ERR_PTR(-ENOMEM);
  43
  44        if (kernfs_ns_enabled(parent))
  45                kn->ns = target->ns;
  46        kn->symlink.target_kn = target;
  47        kernfs_get(target);     /* ref owned by symlink */
  48
  49        error = kernfs_add_one(kn);
  50        if (!error)
  51                return kn;
  52
  53        kernfs_put(kn);
  54        return ERR_PTR(error);
  55}
  56
  57static int kernfs_get_target_path(struct kernfs_node *parent,
  58                                  struct kernfs_node *target, char *path)
  59{
  60        struct kernfs_node *base, *kn;
  61        char *s = path;
  62        int len = 0;
  63
  64        /* go up to the root, stop at the base */
  65        base = parent;
  66        while (base->parent) {
  67                kn = target->parent;
  68                while (kn->parent && base != kn)
  69                        kn = kn->parent;
  70
  71                if (base == kn)
  72                        break;
  73
  74                if ((s - path) + 3 >= PATH_MAX)
  75                        return -ENAMETOOLONG;
  76
  77                strcpy(s, "../");
  78                s += 3;
  79                base = base->parent;
  80        }
  81
  82        /* determine end of target string for reverse fillup */
  83        kn = target;
  84        while (kn->parent && kn != base) {
  85                len += strlen(kn->name) + 1;
  86                kn = kn->parent;
  87        }
  88
  89        /* check limits */
  90        if (len < 2)
  91                return -EINVAL;
  92        len--;
  93        if ((s - path) + len >= PATH_MAX)
  94                return -ENAMETOOLONG;
  95
  96        /* reverse fillup of target string from target to base */
  97        kn = target;
  98        while (kn->parent && kn != base) {
  99                int slen = strlen(kn->name);
 100
 101                len -= slen;
 102                memcpy(s + len, kn->name, slen);
 103                if (len)
 104                        s[--len] = '/';
 105
 106                kn = kn->parent;
 107        }
 108
 109        return 0;
 110}
 111
 112static int kernfs_getlink(struct inode *inode, char *path)
 113{
 114        struct kernfs_node *kn = inode->i_private;
 115        struct kernfs_node *parent = kn->parent;
 116        struct kernfs_node *target = kn->symlink.target_kn;
 117        int error;
 118
 119        mutex_lock(&kernfs_mutex);
 120        error = kernfs_get_target_path(parent, target, path);
 121        mutex_unlock(&kernfs_mutex);
 122
 123        return error;
 124}
 125
 126static 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
 147const 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