fs/overlayfs/namei.c

   1 /*
   2  * Copyright (C) 2011 Novell Inc.
   3  * Copyright (C) 2016 Red Hat, Inc.
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 as published by
   7  * the Free Software Foundation.
   8  */
   9
  10 #include <linux/fs.h>
  11 #include <linux/namei.h>
  12 #include <linux/xattr.h>
  13 #include "overlayfs.h"
  14 #include "ovl_entry.h"
  15
  16 static struct dentry *ovl_lookup_real(struct dentry *dir,
  17                                       const struct qstr *name)
  18 {
  19         struct dentry *dentry;
  20
  21         dentry = lookup_one_len_unlocked(name->name, dir, name->len);
  22         if (IS_ERR(dentry)) {
  23                 if (PTR_ERR(dentry) == -ENOENT ||
  24                     PTR_ERR(dentry) == -ENAMETOOLONG)
  25                         dentry = NULL;
  26         } else if (!dentry->d_inode) {
  27                 dput(dentry);
  28                 dentry = NULL;
  29         } else if (ovl_dentry_weird(dentry)) {
  30                 dput(dentry);
  31                 /* Don't support traversing automounts and other weirdness */
  32                 dentry = ERR_PTR(-EREMOTE);
  33         }
  34         return dentry;
  35 }
  36
  37 static bool ovl_is_opaquedir(struct dentry *dentry)
  38 {
  39         int res;
  40         char val;
  41
  42         if (!d_is_dir(dentry))
  43                 return false;
  44
  45         res = vfs_getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
  46         if (res == 1 && val == 'y')
  47                 return true;
  48
  49         return false;
  50 }
  51
  52 /*
  53  * Returns next layer in stack starting from top.
  54  * Returns -1 if this is the last layer.
  55  */
  56 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
  57 {
  58         struct ovl_entry *oe = dentry->d_fsdata;
  59
  60         BUG_ON(idx < 0);
  61         if (idx == 0) {
  62                 ovl_path_upper(dentry, path);
  63                 if (path->dentry)
  64                         return oe->numlower ? 1 : -1;
  65                 idx++;
  66         }
  67         BUG_ON(idx > oe->numlower);
  68         *path = oe->lowerstack[idx - 1];
  69
  70         return (idx < oe->numlower) ? idx + 1 : -1;
  71 }
  72
  73 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
  74                           unsigned int flags)
  75 {
  76         struct ovl_entry *oe;
  77         const struct cred *old_cred;
  78         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
  79         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
  80         struct path *stack = NULL;
  81         struct dentry *upperdir, *upperdentry = NULL;
  82         unsigned int ctr = 0;
  83         struct inode *inode = NULL;
  84         bool upperopaque = false;
  85         bool stop = false;
  86         bool isdir = false;
  87         struct dentry *this;
  88         unsigned int i;
  89         int err;
  90
  91         if (dentry->d_name.len > ofs->namelen)
  92                 return ERR_PTR(-ENAMETOOLONG);
  93
  94         old_cred = ovl_override_creds(dentry->d_sb);
  95         upperdir = ovl_upperdentry_dereference(poe);
  96         if (upperdir) {
  97                 this = ovl_lookup_real(upperdir, &dentry->d_name);
  98                 err = PTR_ERR(this);
  99                 if (IS_ERR(this))
 100                         goto out;
 101
 102                 if (this) {
 103                         if (unlikely(ovl_dentry_remote(this))) {
 104                                 dput(this);
 105                                 err = -EREMOTE;
 106                                 goto out;
 107                         }
 108                         if (ovl_is_whiteout(this)) {
 109                                 dput(this);
 110                                 this = NULL;
 111                                 stop = upperopaque = true;
 112                         } else if (!d_is_dir(this)) {
 113                                 stop = true;
 114                         } else {
 115                                 isdir = true;
 116                                 if (poe->numlower && ovl_is_opaquedir(this))
 117                                         stop = upperopaque = true;
 118                         }
 119                 }
 120                 upperdentry = this;
 121         }
 122
 123         if (!stop && poe->numlower) {
 124                 err = -ENOMEM;
 125                 stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
 126                 if (!stack)
 127                         goto out_put_upper;
 128         }
 129
 130         for (i = 0; !stop && i < poe->numlower; i++) {
 131                 struct path lowerpath = poe->lowerstack[i];
 132
 133                 this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
 134                 err = PTR_ERR(this);
 135                 if (IS_ERR(this))
 136                         goto out_put;
 137
 138                 if (!this)
 139                         continue;
 140                 if (ovl_is_whiteout(this)) {
 141                         dput(this);
 142                         break;
 143                 }
 144                 /*
 145                  * If this is a non-directory then stop here.
 146                  */
 147                 if (!d_is_dir(this)) {
 148                         if (isdir) {
 149                                 dput(this);
 150                                 break;
 151                         }
 152                         stop = true;
 153                 } else {
 154                         /*
 155                          * Only makes sense to check opaque dir if this is not
 156                          * the lowermost layer.
 157                          */
 158                         if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
 159                                 stop = true;
 160                 }
 161
 162                 stack[ctr].dentry = this;
 163                 stack[ctr].mnt = lowerpath.mnt;
 164                 ctr++;
 165         }
 166
 167         oe = ovl_alloc_entry(ctr);
 168         err = -ENOMEM;
 169         if (!oe)
 170                 goto out_put;
 171
 172         if (upperdentry || ctr) {
 173                 struct dentry *realdentry;
 174                 struct inode *realinode;
 175
 176                 realdentry = upperdentry ? upperdentry : stack[0].dentry;
 177                 realinode = d_inode(realdentry);
 178
 179                 err = -ENOMEM;
 180                 if (upperdentry && !d_is_dir(upperdentry)) {
 181                         inode = ovl_get_inode(dentry->d_sb, realinode);
 182                 } else {
 183                         inode = ovl_new_inode(dentry->d_sb, realinode->i_mode,
 184                                               realinode->i_rdev);
 185                         if (inode)
 186                                 ovl_inode_init(inode, realinode, !!upperdentry);
 187                 }
 188                 if (!inode)
 189                         goto out_free_oe;
 190                 ovl_copyattr(realdentry->d_inode, inode);
 191         }
 192
 193         revert_creds(old_cred);
 194         oe->opaque = upperopaque;
 195         oe->__upperdentry = upperdentry;
 196         memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
 197         kfree(stack);
 198         dentry->d_fsdata = oe;
 199         d_add(dentry, inode);
 200
 201         return NULL;
 202
 203 out_free_oe:
 204         kfree(oe);
 205 out_put:
 206         for (i = 0; i < ctr; i++)
 207                 dput(stack[i].dentry);
 208         kfree(stack);
 209 out_put_upper:
 210         dput(upperdentry);
 211 out:
 212         revert_creds(old_cred);
 213         return ERR_PTR(err);
 214 }
 215
 216 bool ovl_lower_positive(struct dentry *dentry)
 217 {
 218         struct ovl_entry *oe = dentry->d_fsdata;
 219         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 220         const struct qstr *name = &dentry->d_name;
 221         unsigned int i;
 222         bool positive = false;
 223         bool done = false;
 224
 225         /*
 226          * If dentry is negative, then lower is positive iff this is a
 227          * whiteout.
 228          */
 229         if (!dentry->d_inode)
 230                 return oe->opaque;
 231
 232         /* Negative upper -> positive lower */
 233         if (!oe->__upperdentry)
 234                 return true;
 235
 236         /* Positive upper -> have to look up lower to see whether it exists */
 237         for (i = 0; !done && !positive && i < poe->numlower; i++) {
 238                 struct dentry *this;
 239                 struct dentry *lowerdir = poe->lowerstack[i].dentry;
 240
 241                 this = lookup_one_len_unlocked(name->name, lowerdir,
 242                                                name->len);
 243                 if (IS_ERR(this)) {
 244                         switch (PTR_ERR(this)) {
 245                         case -ENOENT:
 246                         case -ENAMETOOLONG:
 247                                 break;
 248
 249                         default:
 250                                 /*
 251                                  * Assume something is there, we just couldn't
 252                                  * access it.
 253                                  */
 254                                 positive = true;
 255                                 break;
 256                         }
 257                 } else {
 258                         if (this->d_inode) {
 259                                 positive = !ovl_is_whiteout(this);
 260                                 done = true;
 261                         }
 262                         dput(this);
 263                 }
 264         }
 265
 266         return positive;
 267 }