ovl: check lowerdir amount for non-upper mount
[sfrench/cifs-2.6.git] / fs / overlayfs / super.c
index f16d318b71f8bbe4e77f8a3214e616101848e49c..edbb3ebcdaadb661befd7af7d8476ab37c3beda0 100644 (file)
@@ -35,7 +35,8 @@ struct ovl_config {
 /* private information held for overlayfs's superblock */
 struct ovl_fs {
        struct vfsmount *upper_mnt;
-       struct vfsmount *lower_mnt;
+       unsigned numlower;
+       struct vfsmount **lower_mnt;
        struct dentry *workdir;
        long lower_namelen;
        /* pathnames of lower and upper dirs, for show_options */
@@ -47,7 +48,6 @@ struct ovl_dir_cache;
 /* private information held for every overlayfs dentry */
 struct ovl_entry {
        struct dentry *__upperdentry;
-       struct dentry *lowerdentry;
        struct ovl_dir_cache *cache;
        union {
                struct {
@@ -56,30 +56,36 @@ struct ovl_entry {
                };
                struct rcu_head rcu;
        };
+       unsigned numlower;
+       struct path lowerstack[];
 };
 
-const char *ovl_opaque_xattr = "trusted.overlay.opaque";
+#define OVL_MAX_STACK 500
 
+static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
+{
+       return oe->numlower ? oe->lowerstack[0].dentry : NULL;
+}
 
 enum ovl_path_type ovl_path_type(struct dentry *dentry)
 {
        struct ovl_entry *oe = dentry->d_fsdata;
+       enum ovl_path_type type = 0;
 
        if (oe->__upperdentry) {
-               if (oe->lowerdentry) {
+               type = __OVL_PATH_UPPER;
+
+               if (oe->numlower) {
                        if (S_ISDIR(dentry->d_inode->i_mode))
-                               return OVL_PATH_MERGE;
-                       else
-                               return OVL_PATH_UPPER;
-               } else {
-                       if (oe->opaque)
-                               return OVL_PATH_UPPER;
-                       else
-                               return OVL_PATH_PURE_UPPER;
+                               type |= __OVL_PATH_MERGE;
+               } else if (!oe->opaque) {
+                       type |= __OVL_PATH_PURE;
                }
        } else {
-               return OVL_PATH_LOWER;
+               if (oe->numlower > 1)
+                       type |= __OVL_PATH_MERGE;
        }
+       return type;
 }
 
 static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
@@ -98,10 +104,9 @@ void ovl_path_upper(struct dentry *dentry, struct path *path)
 
 enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
 {
-
        enum ovl_path_type type = ovl_path_type(dentry);
 
-       if (type == OVL_PATH_LOWER)
+       if (!OVL_TYPE_UPPER(type))
                ovl_path_lower(dentry, path);
        else
                ovl_path_upper(dentry, path);
@@ -120,7 +125,7 @@ struct dentry *ovl_dentry_lower(struct dentry *dentry)
 {
        struct ovl_entry *oe = dentry->d_fsdata;
 
-       return oe->lowerdentry;
+       return __ovl_dentry_lower(oe);
 }
 
 struct dentry *ovl_dentry_real(struct dentry *dentry)
@@ -130,7 +135,7 @@ struct dentry *ovl_dentry_real(struct dentry *dentry)
 
        realdentry = ovl_upperdentry_dereference(oe);
        if (!realdentry)
-               realdentry = oe->lowerdentry;
+               realdentry = __ovl_dentry_lower(oe);
 
        return realdentry;
 }
@@ -143,7 +148,7 @@ struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
        if (realdentry) {
                *is_upper = true;
        } else {
-               realdentry = oe->lowerdentry;
+               realdentry = __ovl_dentry_lower(oe);
                *is_upper = false;
        }
        return realdentry;
@@ -165,11 +170,9 @@ void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
 
 void ovl_path_lower(struct dentry *dentry, struct path *path)
 {
-       struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
        struct ovl_entry *oe = dentry->d_fsdata;
 
-       path->mnt = ofs->lower_mnt;
-       path->dentry = oe->lowerdentry;
+       *path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
 }
 
 int ovl_want_write(struct dentry *dentry)
@@ -249,7 +252,7 @@ static bool ovl_is_opaquedir(struct dentry *dentry)
        if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
                return false;
 
-       res = inode->i_op->getxattr(dentry, ovl_opaque_xattr, &val, 1);
+       res = inode->i_op->getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
        if (res == 1 && val == 'y')
                return true;
 
@@ -261,8 +264,11 @@ static void ovl_dentry_release(struct dentry *dentry)
        struct ovl_entry *oe = dentry->d_fsdata;
 
        if (oe) {
+               unsigned int i;
+
                dput(oe->__upperdentry);
-               dput(oe->lowerdentry);
+               for (i = 0; i < oe->numlower; i++)
+                       dput(oe->lowerstack[i].dentry);
                kfree_rcu(oe, rcu);
        }
 }
@@ -271,9 +277,15 @@ static const struct dentry_operations ovl_dentry_operations = {
        .d_release = ovl_dentry_release,
 };
 
-static struct ovl_entry *ovl_alloc_entry(void)
+static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 {
-       return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
+       size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
+       struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
+
+       if (oe)
+               oe->numlower = numlower;
+
+       return oe;
 }
 
 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
@@ -295,82 +307,154 @@ static inline struct dentry *ovl_lookup_real(struct dentry *dir,
        return dentry;
 }
 
+/*
+ * Returns next layer in stack starting from top.
+ * Returns -1 if this is the last layer.
+ */
+int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
+{
+       struct ovl_entry *oe = dentry->d_fsdata;
+
+       BUG_ON(idx < 0);
+       if (idx == 0) {
+               ovl_path_upper(dentry, path);
+               if (path->dentry)
+                       return oe->numlower ? 1 : -1;
+               idx++;
+       }
+       BUG_ON(idx > oe->numlower);
+       *path = oe->lowerstack[idx - 1];
+
+       return (idx < oe->numlower) ? idx + 1 : -1;
+}
+
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                          unsigned int flags)
 {
        struct ovl_entry *oe;
-       struct dentry *upperdir;
-       struct dentry *lowerdir;
-       struct dentry *upperdentry = NULL;
-       struct dentry *lowerdentry = NULL;
+       struct ovl_entry *poe = dentry->d_parent->d_fsdata;
+       struct path *stack = NULL;
+       struct dentry *upperdir, *upperdentry = NULL;
+       unsigned int ctr = 0;
        struct inode *inode = NULL;
+       bool upperopaque = false;
+       struct dentry *this, *prev = NULL;
+       unsigned int i;
        int err;
 
-       err = -ENOMEM;
-       oe = ovl_alloc_entry();
-       if (!oe)
-               goto out;
-
-       upperdir = ovl_dentry_upper(dentry->d_parent);
-       lowerdir = ovl_dentry_lower(dentry->d_parent);
-
+       upperdir = ovl_upperdentry_dereference(poe);
        if (upperdir) {
-               upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
-               err = PTR_ERR(upperdentry);
-               if (IS_ERR(upperdentry))
-                       goto out_put_dir;
-
-               if (lowerdir && upperdentry) {
-                       if (ovl_is_whiteout(upperdentry)) {
-                               dput(upperdentry);
-                               upperdentry = NULL;
-                               oe->opaque = true;
-                       } else if (ovl_is_opaquedir(upperdentry)) {
-                               oe->opaque = true;
+               this = ovl_lookup_real(upperdir, &dentry->d_name);
+               err = PTR_ERR(this);
+               if (IS_ERR(this))
+                       goto out;
+
+               if (this) {
+                       if (ovl_is_whiteout(this)) {
+                               dput(this);
+                               this = NULL;
+                               upperopaque = true;
+                       } else if (poe->numlower && ovl_is_opaquedir(this)) {
+                               upperopaque = true;
                        }
                }
+               upperdentry = prev = this;
        }
-       if (lowerdir && !oe->opaque) {
-               lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
-               err = PTR_ERR(lowerdentry);
-               if (IS_ERR(lowerdentry))
-                       goto out_dput_upper;
+
+       if (!upperopaque && poe->numlower) {
+               err = -ENOMEM;
+               stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
+               if (!stack)
+                       goto out_put_upper;
        }
 
-       if (lowerdentry && upperdentry &&
-           (!S_ISDIR(upperdentry->d_inode->i_mode) ||
-            !S_ISDIR(lowerdentry->d_inode->i_mode))) {
-               dput(lowerdentry);
-               lowerdentry = NULL;
-               oe->opaque = true;
+       for (i = 0; !upperopaque && i < poe->numlower; i++) {
+               bool opaque = false;
+               struct path lowerpath = poe->lowerstack[i];
+
+               this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
+               err = PTR_ERR(this);
+               if (IS_ERR(this)) {
+                       /*
+                        * If it's positive, then treat ENAMETOOLONG as ENOENT.
+                        */
+                       if (err == -ENAMETOOLONG && (upperdentry || ctr))
+                               continue;
+                       goto out_put;
+               }
+               if (!this)
+                       continue;
+               if (ovl_is_whiteout(this)) {
+                       dput(this);
+                       break;
+               }
+               /*
+                * Only makes sense to check opaque dir if this is not the
+                * lowermost layer.
+                */
+               if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
+                       opaque = true;
+
+               if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
+                            !S_ISDIR(this->d_inode->i_mode))) {
+                       /*
+                        * FIXME: check for upper-opaqueness maybe better done
+                        * in remove code.
+                        */
+                       if (prev == upperdentry)
+                               upperopaque = true;
+                       dput(this);
+                       break;
+               }
+               /*
+                * If this is a non-directory then stop here.
+                */
+               if (!S_ISDIR(this->d_inode->i_mode))
+                       opaque = true;
+
+               stack[ctr].dentry = this;
+               stack[ctr].mnt = lowerpath.mnt;
+               ctr++;
+               prev = this;
+               if (opaque)
+                       break;
        }
 
-       if (lowerdentry || upperdentry) {
+       oe = ovl_alloc_entry(ctr);
+       err = -ENOMEM;
+       if (!oe)
+               goto out_put;
+
+       if (upperdentry || ctr) {
                struct dentry *realdentry;
 
-               realdentry = upperdentry ? upperdentry : lowerdentry;
+               realdentry = upperdentry ? upperdentry : stack[0].dentry;
+
                err = -ENOMEM;
                inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
                                      oe);
                if (!inode)
-                       goto out_dput;
+                       goto out_free_oe;
                ovl_copyattr(realdentry->d_inode, inode);
        }
 
+       oe->opaque = upperopaque;
        oe->__upperdentry = upperdentry;
-       oe->lowerdentry = lowerdentry;
-
+       memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
+       kfree(stack);
        dentry->d_fsdata = oe;
        d_add(dentry, inode);
 
        return NULL;
 
-out_dput:
-       dput(lowerdentry);
-out_dput_upper:
-       dput(upperdentry);
-out_put_dir:
+out_free_oe:
        kfree(oe);
+out_put:
+       for (i = 0; i < ctr; i++)
+               dput(stack[i].dentry);
+       kfree(stack);
+out_put_upper:
+       dput(upperdentry);
 out:
        return ERR_PTR(err);
 }
@@ -383,10 +467,12 @@ struct file *ovl_path_open(struct path *path, int flags)
 static void ovl_put_super(struct super_block *sb)
 {
        struct ovl_fs *ufs = sb->s_fs_info;
+       unsigned i;
 
        dput(ufs->workdir);
        mntput(ufs->upper_mnt);
-       mntput(ufs->lower_mnt);
+       for (i = 0; i < ufs->numlower; i++)
+               mntput(ufs->lower_mnt[i]);
 
        kfree(ufs->config.lowerdir);
        kfree(ufs->config.upperdir);
@@ -400,7 +486,7 @@ static void ovl_put_super(struct super_block *sb)
  * @buf: The struct kstatfs to fill in with stats
  *
  * Get the filesystem statistics.  As writes always target the upper layer
- * filesystem pass the statfs to the same filesystem.
+ * filesystem pass the statfs to the upper filesystem (if it exists)
  */
 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
@@ -409,7 +495,7 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
        struct path path;
        int err;
 
-       ovl_path_upper(root_dentry, &path);
+       ovl_path_real(root_dentry, &path);
 
        err = vfs_statfs(&path, buf);
        if (!err) {
@@ -432,8 +518,21 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
        struct ovl_fs *ufs = sb->s_fs_info;
 
        seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
-       seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
-       seq_printf(m, ",workdir=%s", ufs->config.workdir);
+       if (ufs->config.upperdir) {
+               seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
+               seq_printf(m, ",workdir=%s", ufs->config.workdir);
+       }
+       return 0;
+}
+
+static int ovl_remount(struct super_block *sb, int *flags, char *data)
+{
+       struct ovl_fs *ufs = sb->s_fs_info;
+
+       if (!(*flags & MS_RDONLY) &&
+           (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)))
+               return -EROFS;
+
        return 0;
 }
 
@@ -441,6 +540,7 @@ static const struct super_operations ovl_super_operations = {
        .put_super      = ovl_put_super,
        .statfs         = ovl_statfs,
        .show_options   = ovl_show_options,
+       .remount_fs     = ovl_remount,
 };
 
 enum {
@@ -515,6 +615,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
                        break;
 
                default:
+                       pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
                        return -EINVAL;
                }
        }
@@ -585,24 +686,6 @@ static void ovl_unescape(char *s)
        }
 }
 
-static int ovl_mount_dir(const char *name, struct path *path)
-{
-       int err;
-       char *tmp = kstrdup(name, GFP_KERNEL);
-
-       if (!tmp)
-               return -ENOMEM;
-
-       ovl_unescape(tmp);
-       err = kern_path(tmp, LOOKUP_FOLLOW, path);
-       if (err) {
-               pr_err("overlayfs: failed to resolve '%s': %i\n", tmp, err);
-               err = -EINVAL;
-       }
-       kfree(tmp);
-       return err;
-}
-
 static bool ovl_is_allowed_fs_type(struct dentry *root)
 {
        const struct dentry_operations *dop = root->d_op;
@@ -622,6 +705,75 @@ static bool ovl_is_allowed_fs_type(struct dentry *root)
        return true;
 }
 
+static int ovl_mount_dir_noesc(const char *name, struct path *path)
+{
+       int err = -EINVAL;
+
+       if (!*name) {
+               pr_err("overlayfs: empty lowerdir\n");
+               goto out;
+       }
+       err = kern_path(name, LOOKUP_FOLLOW, path);
+       if (err) {
+               pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
+               goto out;
+       }
+       err = -EINVAL;
+       if (!ovl_is_allowed_fs_type(path->dentry)) {
+               pr_err("overlayfs: filesystem on '%s' not supported\n", name);
+               goto out_put;
+       }
+       if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
+               pr_err("overlayfs: '%s' not a directory\n", name);
+               goto out_put;
+       }
+       return 0;
+
+out_put:
+       path_put(path);
+out:
+       return err;
+}
+
+static int ovl_mount_dir(const char *name, struct path *path)
+{
+       int err = -ENOMEM;
+       char *tmp = kstrdup(name, GFP_KERNEL);
+
+       if (tmp) {
+               ovl_unescape(tmp);
+               err = ovl_mount_dir_noesc(tmp, path);
+               kfree(tmp);
+       }
+       return err;
+}
+
+static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
+                        int *stack_depth)
+{
+       int err;
+       struct kstatfs statfs;
+
+       err = ovl_mount_dir_noesc(name, path);
+       if (err)
+               goto out;
+
+       err = vfs_statfs(path, &statfs);
+       if (err) {
+               pr_err("overlayfs: statfs failed on '%s'\n", name);
+               goto out_put;
+       }
+       *namelen = max(*namelen, statfs.f_namelen);
+       *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
+
+       return 0;
+
+out_put:
+       path_put(path);
+out:
+       return err;
+}
+
 /* Workdir should not be subdir of upperdir and vice versa */
 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 {
@@ -634,16 +786,39 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
        return ok;
 }
 
+static unsigned int ovl_split_lowerdirs(char *str)
+{
+       unsigned int ctr = 1;
+       char *s, *d;
+
+       for (s = d = str;; s++, d++) {
+               if (*s == '\\') {
+                       s++;
+               } else if (*s == ':') {
+                       *d = '\0';
+                       ctr++;
+                       continue;
+               }
+               *d = *s;
+               if (!*s)
+                       break;
+       }
+       return ctr;
+}
+
 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 {
-       struct path lowerpath;
-       struct path upperpath;
-       struct path workpath;
-       struct inode *root_inode;
+       struct path upperpath = { NULL, NULL };
+       struct path workpath = { NULL, NULL };
        struct dentry *root_dentry;
        struct ovl_entry *oe;
        struct ovl_fs *ufs;
-       struct kstatfs statfs;
+       struct path *stack = NULL;
+       char *lowertmp;
+       char *lower;
+       unsigned int numlower;
+       unsigned int stacklen = 0;
+       unsigned int i;
        int err;
 
        err = -ENOMEM;
@@ -655,123 +830,141 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
        if (err)
                goto out_free_config;
 
-       /* FIXME: workdir is not needed for a R/O mount */
        err = -EINVAL;
-       if (!ufs->config.upperdir || !ufs->config.lowerdir ||
-           !ufs->config.workdir) {
-               pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
+       if (!ufs->config.lowerdir) {
+               pr_err("overlayfs: missing 'lowerdir'\n");
                goto out_free_config;
        }
 
-       err = -ENOMEM;
-       oe = ovl_alloc_entry();
-       if (oe == NULL)
-               goto out_free_config;
-
-       err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
-       if (err)
-               goto out_free_oe;
-
-       err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
-       if (err)
-               goto out_put_upperpath;
+       sb->s_stack_depth = 0;
+       if (ufs->config.upperdir) {
+               /* FIXME: workdir is not needed for a R/O mount */
+               if (!ufs->config.workdir) {
+                       pr_err("overlayfs: missing 'workdir'\n");
+                       goto out_free_config;
+               }
 
-       err = ovl_mount_dir(ufs->config.workdir, &workpath);
-       if (err)
-               goto out_put_lowerpath;
+               err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
+               if (err)
+                       goto out_free_config;
 
-       err = -EINVAL;
-       if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
-           !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
-           !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
-               pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
-               goto out_put_workpath;
-       }
+               err = ovl_mount_dir(ufs->config.workdir, &workpath);
+               if (err)
+                       goto out_put_upperpath;
 
-       if (upperpath.mnt != workpath.mnt) {
-               pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
-               goto out_put_workpath;
+               err = -EINVAL;
+               if (upperpath.mnt != workpath.mnt) {
+                       pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
+                       goto out_put_workpath;
+               }
+               if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
+                       pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
+                       goto out_put_workpath;
+               }
+               sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
        }
-       if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
-               pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
+       err = -ENOMEM;
+       lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
+       if (!lowertmp)
                goto out_put_workpath;
-       }
 
-       if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
-               pr_err("overlayfs: filesystem of upperdir is not supported\n");
-               goto out_put_workpath;
+       err = -EINVAL;
+       stacklen = ovl_split_lowerdirs(lowertmp);
+       if (stacklen > OVL_MAX_STACK) {
+               pr_err("overlayfs: too many lower directries, limit is %d\n",
+                      OVL_MAX_STACK);
+               goto out_free_lowertmp;
+       } else if (!ufs->config.upperdir && stacklen == 1) {
+               pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
+               goto out_free_lowertmp;
        }
 
-       if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
-               pr_err("overlayfs: filesystem of lowerdir is not supported\n");
-               goto out_put_workpath;
-       }
+       stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
+       if (!stack)
+               goto out_free_lowertmp;
 
-       err = vfs_statfs(&lowerpath, &statfs);
-       if (err) {
-               pr_err("overlayfs: statfs failed on lowerpath\n");
-               goto out_put_workpath;
-       }
-       ufs->lower_namelen = statfs.f_namelen;
+       lower = lowertmp;
+       for (numlower = 0; numlower < stacklen; numlower++) {
+               err = ovl_lower_dir(lower, &stack[numlower],
+                                   &ufs->lower_namelen, &sb->s_stack_depth);
+               if (err)
+                       goto out_put_lowerpath;
 
-       sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
-                               lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
+               lower = strchr(lower, '\0') + 1;
+       }
 
        err = -EINVAL;
+       sb->s_stack_depth++;
        if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
                pr_err("overlayfs: maximum fs stacking depth exceeded\n");
-               goto out_put_workpath;
+               goto out_put_lowerpath;
        }
 
-       ufs->upper_mnt = clone_private_mount(&upperpath);
-       err = PTR_ERR(ufs->upper_mnt);
-       if (IS_ERR(ufs->upper_mnt)) {
-               pr_err("overlayfs: failed to clone upperpath\n");
-               goto out_put_workpath;
-       }
+       if (ufs->config.upperdir) {
+               ufs->upper_mnt = clone_private_mount(&upperpath);
+               err = PTR_ERR(ufs->upper_mnt);
+               if (IS_ERR(ufs->upper_mnt)) {
+                       pr_err("overlayfs: failed to clone upperpath\n");
+                       goto out_put_lowerpath;
+               }
 
-       ufs->lower_mnt = clone_private_mount(&lowerpath);
-       err = PTR_ERR(ufs->lower_mnt);
-       if (IS_ERR(ufs->lower_mnt)) {
-               pr_err("overlayfs: failed to clone lowerpath\n");
-               goto out_put_upper_mnt;
+               ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
+               err = PTR_ERR(ufs->workdir);
+               if (IS_ERR(ufs->workdir)) {
+                       pr_err("overlayfs: failed to create directory %s/%s\n",
+                              ufs->config.workdir, OVL_WORKDIR_NAME);
+                       goto out_put_upper_mnt;
+               }
        }
 
-       ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
-       err = PTR_ERR(ufs->workdir);
-       if (IS_ERR(ufs->workdir)) {
-               pr_err("overlayfs: failed to create directory %s/%s\n",
-                      ufs->config.workdir, OVL_WORKDIR_NAME);
-               goto out_put_lower_mnt;
-       }
+       err = -ENOMEM;
+       ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
+       if (ufs->lower_mnt == NULL)
+               goto out_put_workdir;
+       for (i = 0; i < numlower; i++) {
+               struct vfsmount *mnt = clone_private_mount(&stack[i]);
 
-       /*
-        * Make lower_mnt R/O.  That way fchmod/fchown on lower file
-        * will fail instead of modifying lower fs.
-        */
-       ufs->lower_mnt->mnt_flags |= MNT_READONLY;
+               err = PTR_ERR(mnt);
+               if (IS_ERR(mnt)) {
+                       pr_err("overlayfs: failed to clone lowerpath\n");
+                       goto out_put_lower_mnt;
+               }
+               /*
+                * Make lower_mnt R/O.  That way fchmod/fchown on lower file
+                * will fail instead of modifying lower fs.
+                */
+               mnt->mnt_flags |= MNT_READONLY;
+
+               ufs->lower_mnt[ufs->numlower] = mnt;
+               ufs->numlower++;
+       }
 
-       /* If the upper fs is r/o, we mark overlayfs r/o too */
-       if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
+       /* If the upper fs is r/o or nonexistent, we mark overlayfs r/o too */
+       if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
                sb->s_flags |= MS_RDONLY;
 
        sb->s_d_op = &ovl_dentry_operations;
 
        err = -ENOMEM;
-       root_inode = ovl_new_inode(sb, S_IFDIR, oe);
-       if (!root_inode)
-               goto out_put_workdir;
+       oe = ovl_alloc_entry(numlower);
+       if (!oe)
+               goto out_put_lower_mnt;
 
-       root_dentry = d_make_root(root_inode);
+       root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
        if (!root_dentry)
-               goto out_put_workdir;
+               goto out_free_oe;
 
        mntput(upperpath.mnt);
-       mntput(lowerpath.mnt);
+       for (i = 0; i < numlower; i++)
+               mntput(stack[i].mnt);
        path_put(&workpath);
+       kfree(lowertmp);
 
        oe->__upperdentry = upperpath.dentry;
-       oe->lowerdentry = lowerpath.dentry;
+       for (i = 0; i < numlower; i++) {
+               oe->lowerstack[i].dentry = stack[i].dentry;
+               oe->lowerstack[i].mnt = ufs->lower_mnt[i];
+       }
 
        root_dentry->d_fsdata = oe;
 
@@ -782,20 +975,26 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
        return 0;
 
+out_free_oe:
+       kfree(oe);
+out_put_lower_mnt:
+       for (i = 0; i < ufs->numlower; i++)
+               mntput(ufs->lower_mnt[i]);
+       kfree(ufs->lower_mnt);
 out_put_workdir:
        dput(ufs->workdir);
-out_put_lower_mnt:
-       mntput(ufs->lower_mnt);
 out_put_upper_mnt:
        mntput(ufs->upper_mnt);
+out_put_lowerpath:
+       for (i = 0; i < numlower; i++)
+               path_put(&stack[i]);
+       kfree(stack);
+out_free_lowertmp:
+       kfree(lowertmp);
 out_put_workpath:
        path_put(&workpath);
-out_put_lowerpath:
-       path_put(&lowerpath);
 out_put_upperpath:
        path_put(&upperpath);
-out_free_oe:
-       kfree(oe);
 out_free_config:
        kfree(ufs->config.lowerdir);
        kfree(ufs->config.upperdir);