fs/overlayfs/inode.c

   1 /*
   2  *
   3  * Copyright (C) 2011 Novell 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/slab.h>
  12 #include <linux/cred.h>
  13 #include <linux/xattr.h>
  14 #include <linux/posix_acl.h>
  15 #include "overlayfs.h"
  16
  17 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
  18 {
  19         int err;
  20         struct dentry *upperdentry;
  21         const struct cred *old_cred;
  22
  23         /*
  24          * Check for permissions before trying to copy-up.  This is redundant
  25          * since it will be rechecked later by ->setattr() on upper dentry.  But
  26          * without this, copy-up can be triggered by just about anybody.
  27          *
  28          * We don't initialize inode->size, which just means that
  29          * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
  30          * check for a swapfile (which this won't be anyway).
  31          */
  32         err = setattr_prepare(dentry, attr);
  33         if (err)
  34                 return err;
  35
  36         err = ovl_want_write(dentry);
  37         if (err)
  38                 goto out;
  39
  40         err = ovl_copy_up(dentry);
  41         if (!err) {
  42                 upperdentry = ovl_dentry_upper(dentry);
  43
  44                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
  45                         attr->ia_valid &= ~ATTR_MODE;
  46
  47                 inode_lock(upperdentry->d_inode);
  48                 old_cred = ovl_override_creds(dentry->d_sb);
  49                 err = notify_change(upperdentry, attr, NULL);
  50                 revert_creds(old_cred);
  51                 if (!err)
  52                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
  53                 inode_unlock(upperdentry->d_inode);
  54         }
  55         ovl_drop_write(dentry);
  56 out:
  57         return err;
  58 }
  59
  60 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
  61                          struct kstat *stat)
  62 {
  63         struct path realpath;
  64         const struct cred *old_cred;
  65         int err;
  66
  67         ovl_path_real(dentry, &realpath);
  68         old_cred = ovl_override_creds(dentry->d_sb);
  69         err = vfs_getattr(&realpath, stat);
  70         revert_creds(old_cred);
  71         return err;
  72 }
  73
  74 int ovl_permission(struct inode *inode, int mask)
  75 {
  76         bool is_upper;
  77         struct inode *realinode = ovl_inode_real(inode, &is_upper);
  78         const struct cred *old_cred;
  79         int err;
  80
  81         /* Careful in RCU walk mode */
  82         if (!realinode) {
  83                 WARN_ON(!(mask & MAY_NOT_BLOCK));
  84                 return -ECHILD;
  85         }
  86
  87         /*
  88          * Check overlay inode with the creds of task and underlying inode
  89          * with creds of mounter
  90          */
  91         err = generic_permission(inode, mask);
  92         if (err)
  93                 return err;
  94
  95         old_cred = ovl_override_creds(inode->i_sb);
  96         if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
  97                 mask &= ~(MAY_WRITE | MAY_APPEND);
  98                 /* Make sure mounter can read file for copy up later */
  99                 mask |= MAY_READ;
 100         }
 101         err = inode_permission(realinode, mask);
 102         revert_creds(old_cred);
 103
 104         return err;
 105 }
 106
 107 static const char *ovl_get_link(struct dentry *dentry,
 108                                 struct inode *inode,
 109                                 struct delayed_call *done)
 110 {
 111         const struct cred *old_cred;
 112         const char *p;
 113
 114         if (!dentry)
 115                 return ERR_PTR(-ECHILD);
 116
 117         old_cred = ovl_override_creds(dentry->d_sb);
 118         p = vfs_get_link(ovl_dentry_real(dentry), done);
 119         revert_creds(old_cred);
 120         return p;
 121 }
 122
 123 bool ovl_is_private_xattr(const char *name)
 124 {
 125         return strncmp(name, OVL_XATTR_PREFIX,
 126                        sizeof(OVL_XATTR_PREFIX) - 1) == 0;
 127 }
 128
 129 int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
 130                   size_t size, int flags)
 131 {
 132         int err;
 133         struct path realpath;
 134         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 135         const struct cred *old_cred;
 136
 137         err = ovl_want_write(dentry);
 138         if (err)
 139                 goto out;
 140
 141         if (!value && !OVL_TYPE_UPPER(type)) {
 142                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 143                 if (err < 0)
 144                         goto out_drop_write;
 145         }
 146
 147         err = ovl_copy_up(dentry);
 148         if (err)
 149                 goto out_drop_write;
 150
 151         if (!OVL_TYPE_UPPER(type))
 152                 ovl_path_upper(dentry, &realpath);
 153
 154         old_cred = ovl_override_creds(dentry->d_sb);
 155         if (value)
 156                 err = vfs_setxattr(realpath.dentry, name, value, size, flags);
 157         else {
 158                 WARN_ON(flags != XATTR_REPLACE);
 159                 err = vfs_removexattr(realpath.dentry, name);
 160         }
 161         revert_creds(old_cred);
 162
 163 out_drop_write:
 164         ovl_drop_write(dentry);
 165 out:
 166         return err;
 167 }
 168
 169 int ovl_xattr_get(struct dentry *dentry, const char *name,
 170                   void *value, size_t size)
 171 {
 172         struct dentry *realdentry = ovl_dentry_real(dentry);
 173         ssize_t res;
 174         const struct cred *old_cred;
 175
 176         old_cred = ovl_override_creds(dentry->d_sb);
 177         res = vfs_getxattr(realdentry, name, value, size);
 178         revert_creds(old_cred);
 179         return res;
 180 }
 181
 182 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 183 {
 184         struct dentry *realdentry = ovl_dentry_real(dentry);
 185         ssize_t res;
 186         size_t len;
 187         char *s;
 188         const struct cred *old_cred;
 189
 190         old_cred = ovl_override_creds(dentry->d_sb);
 191         res = vfs_listxattr(realdentry, list, size);
 192         revert_creds(old_cred);
 193         if (res <= 0 || size == 0)
 194                 return res;
 195
 196         /* filter out private xattrs */
 197         for (s = list, len = res; len;) {
 198                 size_t slen = strnlen(s, len) + 1;
 199
 200                 /* underlying fs providing us with an broken xattr list? */
 201                 if (WARN_ON(slen > len))
 202                         return -EIO;
 203
 204                 len -= slen;
 205                 if (ovl_is_private_xattr(s)) {
 206                         res -= slen;
 207                         memmove(s, s + slen, len);
 208                 } else {
 209                         s += slen;
 210                 }
 211         }
 212
 213         return res;
 214 }
 215
 216 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 217 {
 218         struct inode *realinode = ovl_inode_real(inode, NULL);
 219         const struct cred *old_cred;
 220         struct posix_acl *acl;
 221
 222         if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
 223                 return NULL;
 224
 225         old_cred = ovl_override_creds(inode->i_sb);
 226         acl = get_acl(realinode, type);
 227         revert_creds(old_cred);
 228
 229         return acl;
 230 }
 231
 232 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 233                                   struct dentry *realdentry)
 234 {
 235         if (OVL_TYPE_UPPER(type))
 236                 return false;
 237
 238         if (special_file(realdentry->d_inode->i_mode))
 239                 return false;
 240
 241         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 242                 return false;
 243
 244         return true;
 245 }
 246
 247 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 248 {
 249         int err = 0;
 250         struct path realpath;
 251         enum ovl_path_type type;
 252
 253         type = ovl_path_real(dentry, &realpath);
 254         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 255                 err = ovl_want_write(dentry);
 256                 if (!err) {
 257                         err = ovl_copy_up_flags(dentry, file_flags);
 258                         ovl_drop_write(dentry);
 259                 }
 260         }
 261
 262         return err;
 263 }
 264
 265 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
 266 {
 267         struct dentry *alias;
 268         struct path upperpath;
 269
 270         if (!(flags & S_ATIME))
 271                 return 0;
 272
 273         alias = d_find_any_alias(inode);
 274         if (!alias)
 275                 return 0;
 276
 277         ovl_path_upper(alias, &upperpath);
 278         if (upperpath.dentry) {
 279                 touch_atime(&upperpath);
 280                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
 281         }
 282
 283         dput(alias);
 284
 285         return 0;
 286 }
 287
 288 static const struct inode_operations ovl_file_inode_operations = {
 289         .setattr        = ovl_setattr,
 290         .permission     = ovl_permission,
 291         .getattr        = ovl_getattr,
 292         .listxattr      = ovl_listxattr,
 293         .get_acl        = ovl_get_acl,
 294         .update_time    = ovl_update_time,
 295 };
 296
 297 static const struct inode_operations ovl_symlink_inode_operations = {
 298         .setattr        = ovl_setattr,
 299         .get_link       = ovl_get_link,
 300         .getattr        = ovl_getattr,
 301         .listxattr      = ovl_listxattr,
 302         .update_time    = ovl_update_time,
 303 };
 304
 305 static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev)
 306 {
 307         inode->i_ino = get_next_ino();
 308         inode->i_mode = mode;
 309         inode->i_flags |= S_NOCMTIME;
 310 #ifdef CONFIG_FS_POSIX_ACL
 311         inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
 312 #endif
 313
 314         switch (mode & S_IFMT) {
 315         case S_IFREG:
 316                 inode->i_op = &ovl_file_inode_operations;
 317                 break;
 318
 319         case S_IFDIR:
 320                 inode->i_op = &ovl_dir_inode_operations;
 321                 inode->i_fop = &ovl_dir_operations;
 322                 break;
 323
 324         case S_IFLNK:
 325                 inode->i_op = &ovl_symlink_inode_operations;
 326                 break;
 327
 328         default:
 329                 inode->i_op = &ovl_file_inode_operations;
 330                 init_special_inode(inode, mode, rdev);
 331                 break;
 332         }
 333 }
 334
 335 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev)
 336 {
 337         struct inode *inode;
 338
 339         inode = new_inode(sb);
 340         if (inode)
 341                 ovl_fill_inode(inode, mode, rdev);
 342
 343         return inode;
 344 }
 345
 346 static int ovl_inode_test(struct inode *inode, void *data)
 347 {
 348         return ovl_inode_real(inode, NULL) == data;
 349 }
 350
 351 static int ovl_inode_set(struct inode *inode, void *data)
 352 {
 353         inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
 354         return 0;
 355 }
 356
 357 struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
 358
 359 {
 360         struct inode *inode;
 361
 362         inode = iget5_locked(sb, (unsigned long) realinode,
 363                              ovl_inode_test, ovl_inode_set, realinode);
 364         if (inode && inode->i_state & I_NEW) {
 365                 ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev);
 366                 set_nlink(inode, realinode->i_nlink);
 367                 unlock_new_inode(inode);
 368         }
 369
 370         return inode;
 371 }